•ELEMENTS
PHILOSOPHY,
ARRANGED UNDER THE FOLLOWING
HE ADS t
Matter and Motion, The Universe, The Solar System, The Fixed Stars
e xe tars,
The Earth considered as a Planet, The Atmosphere,
Meteors,
Springs, Rivers, and the Sea,
Fossils,
Plants,
Animals.,
The Human Frame,
And THE HUMAN UNDERSTANDING,
T see a mighty arm, by man unseen, '•Resistless-, not to be controlled, that guides, " In solitude of unshar'd energies, u All these thy ceaseless miracles, O world!"
C. LAME-
NEW-rORK:
Printed by D. & G. Bruce, FOR J. QSBQRN, BOOKSELLER, 13 PARK,
• 1808,
CONTENTS;"
Page
Ckap. I. Matter and Motion . , . 11
II. The Universe 24>
III. The Solar System 3f
IV. The Fixed Stars 57
V. The Earth considered as a Planet . . 68
VI. The Atmosphere 90
VII. Meteors • . . . , 105
VIII. Springs, Rivers, and the Sea 124
IX. Fossils 141
X. Plants 177
XI. Animals 200
XII. The Human Frame 234
XIII. The Human Understanding ...... ^260
984
PREFACE.
IN an age like the present, when the growth of every production con- ducive to the interests of morality, and a more extensive knowledge of the Creator through the medium of his
O 'y
tvorks, is recommended and publicly encouraged, hut little need be offered by way of apology for the present Compilation. One important object of the following pages was to present ^ in a very compact and comprehensive form, an interesting and connected account of those laws and operaiions in the material world > which > under the elaborate pens of philosophical authors, cover an extent of scientific ground too enlarged for the commer- cial and labouring individual to tra- vel over ;— but more particularly has this little compendium been arranged for the juvenile inquirer, who either A
PREFACE.
from a premature wish to anticijh the result of deep calculations, or from, other contingent occupations, would have a general, yet clear, idea of ob- jects, which zvithout the aid of philo- sophy he cannot understand. To en- able him to accomplish this desirable end, the following pages are, as far as possible, divested of the technical difficulties which but too often form impenetrable barriers to the expan- sion of the rising mind. While, how- ever, they endeavour to exhibit in a -^amiliar manner that chain of con- nexion which binds and unites all na- ture, they will by no means supersede an encouragement to penetrate into those sciences whence the axioms, laws, and calculations which relate to mat- ter and motion are ascertained..
Having notified the design of this little manuel, it is unnecessary to en- force the importance of the. subject of which it treats. No employment sure-
PREFACE. 7
hj yields so rich a 'harvest of instruc- tion and delight to a rational being as that of surveying the wonderful works of tlic Great Creator -, as dis- played in the various parts of the universe. Such employment is a source of never-failing satisfaction to per- sons of every age ; and it is only by acquiring a knowledge of nature, and observing the contrivance and skill conspicuous in every department of creation, that we are enabled to form an adequate idea of the attributes and character of the Supreme Being. In proportion as we attain a know- ledge of the objects around us they become interesting and important. That which to the careless and un- enlightened spectator •, appears solita- ry and detached, having no other con- nection with the rest of the universe but the shadowy andjleeting relation of co-existence, zvill, to him who takes i glimpse into the general economy
$ PREFACE*
of nature* declare themselves to l>e ports of a great and harmonious whole, connected by general laws, and tending fo one general and beneficent J);trp-jse> and cannot fail of impres- sing him with a wish to co-operate in tins glorious plan, by acting worthy of the place he holds among the works
&GO&
Tn as is the study of nature calcu- lated to eral1 the mind, and reduce the sinn of human pride and igno- ? ' - , and ccmes in aid of that self- abasement which the great duties of Christianity impose, hy teaching man that, though he stands a pinnacle of power, and grasps in intellect all the prodigious works of 'creation, he is but a link in an immeasurable chain that serve* to suspend and give motion to the zoorks of Him who
Connects each being, greatest with the least, Made beast in aid of man, and man of beast.
Nor is it as a moral agent only
PREFACE.
tnat man is benefited by a knowledge of natural philosophy ; it teaches him to employ the powers of nature to the greatest advantage for the embellish- ment and comfort of life, and extends his empire over the material universe.
Knowledge of this kind, therefore, is the most valuable that man can ac- quire: it enriches his life with conve- niences, enlarges his views, and lays' a foundation for the most rational and exalted piety. *( The universe (says Boyle) is the magnificent tem- ple of its great Author ; and man is ordained, by his powers and qualifi- cations, the high-priest of nature, to celebrate divine service in this temple of the universe."
Let him then, aspiring to the dig- nity of his station, assisted by the writings of modern authors, devote his noblest powers to the investigation of the laws of nature ; and evince that he is not in vain given ability to be
1O PREFACE*
wiser than the fowls of heaven, and to have more understanding than the beasts which perish.
ELEMENTS
NATURAL PHILOSOPHY,
CHAP. I.
Of Matter and Motion.
MATTER is an extended solid* sub- stance ; which being comprehended un- der distinct surfaces, makes so many par* ticular distinct bodies.
* Solidity is not here considered as opposed to fluidity, but as that property which every body possesses of not permitting' any other substance to occupy the same place with it at the same time ; so that both water and air, and every other fluid, are equally solid, in this sense of the word, with the hardest body. By solidity, in common lan- guage, is understood the property of not being* easily separated into parts ; and therefore the reader must be careful not to confound the mean- ing- of the popular with the philosophical terro*
1 2 Matter and Motion.
Motion is so well known by the sight and touch, that to use words to give a clearer idea of it would be in vain.
Matter, or body, is indifferent to mo- tion or rest.
There is as much force required to put a body, which is in motion, at rest ; as there is to set a body, which is at rest, into motion.
No parcel of matter can give itself ei- ther motion or rest ; and therefore a bo- dy at rest will remain so eternally, ex- cept some external cause puts it in mo- tion ; and a body in motion will move eternally, except some external cause stops it.
A body in motion will always move on in a straight line, unless it be turned out of it by some external cause ; because a body can no more alter the determina- tion of its motion than it can begin it, alter or stop its motion itself.
The velocity of motion is estimated by the time employed in moving over a certain space, or by the space moved over in a certain time. The less the time, and the greater the space moved over, the greater is the velocity ; on the contrary,
Matter and Motion. 13
the greater the time,and the less the space moved over, th*. less is the velocity* Ev- ery body in motion must have a determi- nate velocity. To ascertain the degree of this swiftness or velocity, the space run over must be divided by the time. For example, suppose a body moves over 1000 yards in 10 minutes, its velocity will be 100 yards per minute, because 100 is the quotient of 1000, divided by 10. If we would compare the velocity of twu bodies A and B, of v.hich A moves over 54 yards in 9 minutes, and B 96 yards in 6 minutes, the velocity of A will he to that of B, in the proportion of 6 (the quotient of 54 divided by 9) to 16 (the quotient of 96 divided by 6.)
To know the space run over, the velo- city must be multiplied by the time ; for it is evident, that if either the velocity or the time be increased, the space run over will be greater. If the velocity be doub- led, then the body will move over twice the space in the same time ; or if the time be twice as great, then the space will be doubled : but if the velocity and time be both doubled, then will the be four times as great,
14 Matter and Motion.
It follows from this, that when two bodies move over unequal spaces in un- equal times, their velocities are to each other as the quotients arising from divi- ding the spaces run over by the times. If two bodies move over unequal spaces in the same time, their velocities will be in proportion to the spaces passed over. And if two bodies move over equal spa- ces in unequal times, then their respec- tive velocities will be inversely as the time employed ; that is, if A in one min- ute, and B in two minutes, run over 10O yards, the velocity of A will be to that "of B as 2 to 1 .
It appears, as far as human obervation reaches, to be a settled law of nature, that u all bodies have a tendency, attrac- tion, or gravitation towards one another."
The same force applied to two differ- ent bodies, produces always the same quantity of motion in each of them. For instance, let a boat, which with its lad- ing is one tun, be tied at a distance, to another vessel, which with its lading is twenty-six tuns ; if the rope that ties tliem together be pulled either in the less or bigger of these vessels, the
Matter and Motion. 15
two, in their approach one to another, ivijl move twenty-six foot, while the oth- er moves but one foot.
Wherefore the quantity of matter in the earth being twenty-six times more than in the moon, the motion in the moon towards the earth, by the common force of attraction, by which they are impelled towards one another, will be twenty-six times as fast as in the earth ; that is, the moon will move twenty-six miles towards the earth, for every mile the earth moves towards the moon.
This attraction is the strongest, the nearer the attracting bodies are to each other ; and in different distances of the same bodies, is reciprocally in the dupli- cate proportion of those distances. For instance, if two bodies, at a given dis- tance, attract each other with a certain force, at half the distance, they will at- tract each other with four times that force ; at one third of the distance, with nine times that force ; and so on.
Two bodies, at a distance, will put one •another into motion by the force of at- traction ; which is inexplicable by us, though made evident to us by experience,
16 Matter and Motion*
and so to be taken as a principle in na* tural philosophy.
Supposing then the earth the sole bo- dy in the universe, and at rest ; if God should create the ir.oon, at the same dis- tance that it is now from the earth, the earth and the moon would presently be- gin to move one towards another in a straight line, by this motion of attraction or gravitation.
If a body, that by the attraction of another would move in a straight line towards it, receives a new motion any ways oblique to the first, it will no longer move in a straight line, according to ei- ther of those directions, but in a curve, that will partake of both ; and this curve will differ, according to the nature and quantity of the forces that concurred to produce it; as, for instance, in many ca- ses it will be such a curve as ends when* it began, or recurs into itself; that is, make up a circle, or an ellipsis, or oval very little differing from a circle.
Attraction may be divided, with res- pect to the law it observes, into two kinds. That which takes place at a sensible, dis- tance^ and that which does not extend to
Matter and Motion* 1 7
sensible distances. The first is called the attraction of gravity, or, by mathe- maticians, the centripetal force.
This is the species of attraction whose laws we have endeavoured to elucidate. It is one of the most universal principles In nature. We see and feel it operate in bodies near the earth, and find by obser- vation that the same power (i. e. a power which acts in the same manner, and by the same rules, viz. always proportionally to the quantities of mattter, and inverse- ly as the squares of the distances) does al- so obtain in the moon, and the other plan- ets, both primary and secondary, as well as in the comets ; and even that this is the very power by which they are all re- tained in their orbits. This mighty prin- ciple fornixS the earth into a round and dense ball, holds every thing animate and inanimate to its surface, and makes its whole surface its general top.
.From this attraction arises all the mo- tion, and consequently all the mutation, in the great world. By this heavy bodies descend, and light ones ascend ; by this projectiles are directed, vapours and ex- halations rise, and rains fall -, by this B
1 8 Matter and Motion.
rivers glide, the ocean swells, the air presses, &c.
2d. That which does not extend to sensible distances. Such is found to ob- tain in the minute particles of which bodies are composed, attracting each oth- er at or extremely near the point of con- tact, with forces often much superior to that of gravity, but which at any distance decrease much faster than the power of gravity. This power a late ingenious author calls the attraction of cohesion, as being that by which the atoms or in- sensible particles of bodies are united into sensible masses.
The laws of motion, percussion, &c* in sensible bodies, under various circum- stances, as falling, projected, &c. do not reach those more recluse intestine mo- tions in the component particles of the same bodies, on which depend the chan- ges in the texture, colour, properties,. &c. of bodies. So that our philosophy, if it were only founded on the principle of gravitation, and even carried as far as this would kad us, would still be very deficient. But, besides the common law* of sensible masses, the minute parts they
Matter and Motion. 19
are composed of are found subject to some others, which have but lately been noticed,, and are even yet imperfectly known8 Newton himself, to whose hap- py penetration we owe the hint, limits liimself with establishing that there are such motions in the minima natures, and that they flow from certain powers or forces, not reducible to any of those in the great world, and from hence he ac- counts for an infinity of phenomena, oth- erwise inexplicable, to which the princi- ple of gravity is inadequate. Thus, adds Sir Isaac, "will nature be found very conformable to herself, and very simple; performing all the great motions of the heavenly bodies by the attraction of grav- ity, which intercedes those bodies, and almost all the small ones of their parts, by some other attractive power diffused through their particles. Without such principles, there never would have been any motion in the world ; and without the continuance of it, motion would soon perish, there being otherwise a great de- crease or diminution, of it, which is only supplied by these active principles." By the attraction of cohesion are form-
2O liter and Motion.
cd stones, metals, woods, salts, and eve- ry thing that may be denominated body. The effects of solders, glue, cements, &c. are all from the same cause. So jewels, hard stones, stalactites, petrifactions, por- celain, pottery, bricks, flags, glass, ce- ments, artificial stones, and plastic earthy compositions, which preserve their figure in drying, all are children of this great agent ; and as this power is much great- er in some bodies than in others, there arises an infinite variety in the strength, the weight, the texture, &c. of metals, stones, &c. for we have powerful reasons to believe that the original particles of all matter are of the same weight ; and that it is this principle that makes thegreat dif- ference in their specific weight. To minds not used to philosophical investigation, it must appear a bold assertion to say, that the particles of gold are not one whit hea- vier than the particles of cork ; but expe- riment and observation shew this to be really the case.
The grand antagonist principle of the attraction of cohesion is fire (or caloric in the new language of chemistry.) These two opposing powers keep nature in a state
Matter and Motion. 21
«f perpetual motion. When the attractive force is strongest, the body continues in a state of solidity ; but if, on the contrary, heat has so far removed the particles of it, as to place them beyond the sphere of at- traction they lose their adhesion, and the body becomes fluid. Water, when cooled below 32 degrees of Fahrenheit's ther- mometer, becomes solid, and is called ice. Above that temperature, its parti- cles not being held together, it becomes liquid ; but when raised to 212 degrees, its particles give way to the repulsive power of fire, and, flying off, assume an aeriform state, called steam ; the same may be affirmed of all bodies in nature, for even diamonds, the hardest substance we know, are capable of being dispersed by a common culinary fire*
It may therefore be considered as an axiom, that all bodies are capable in cer- tain circumstances, of the three states of !$gtidity\ fluidity^ and gas.
The atoms of which bodies are formed, are concealed from us by their minute- ness, and though they are the active parts of matter, and the great instruments of Bature,on which depend all its operations* B2
32 Matter and Motion.
we can form no idea of them, for whether we view animate or inanimate matter, the corpuscles of which it is formed ^re so infinitely small, as not only to escape the scrutiny of the highest magnifying powers in glasses, but even imagination itself is incapable of forming an idea of an original particle of matter : One pound of gold is capable of covering a wire that will circumscribe the globe, nay, so infi- nite is this divisibility that Lewenhoeck discovered more living animalcules in the milt of on^ single cod-fish than there are jnen, women, and children on the face of the earth ! and those so small that many thousands may stand upon the point of a needle. And if we suppose that these animalculae are furnished with blood, like other animals, and if the globules of their blood bear the same proportion to their bulk as those of a man bear to his body, it may be proved, that the smallest visible grain of sand would contain more of these globules than 10,256 of the largest moun- tains in the world would contain grains of sand.
When we consider these tilings we seem to look down into infinity j and as.
Matter and Motion. 23
in the contemplation of the starry heavens, we can conceive no term to the extension of space ; so, in regarding the minute parts of creation we see no end to the divisibility of matter. We are lost in wonder when we attempt to comprehend either the vastness or the minuteness of creation, and are necessarily made to feel that it belongs only to the one great and incomprehensible Power, who work- eth in ways past finding out.
24 The Universe*
CHAP. II.
Of the Universe.
TO any one, who looks about him in the world, there at:e obvious several dis- tinct masses of matter, separate from one another ; some whereof have discernable motions. These are the sun, the fixed stars, the comets, and the planets, amongst which this earth, which we inhabit, is one. All these are visible to our naked eyes.
Besides these, telescopes have discov« ered several fixed stars, invisible to the naked eye ; and several other bodies mo- ving about some of the planets ; all which were invisible and unknown, before the use of prospective glasses was found.
The vast distances between these great bodies, are called intermundane spaces ; in which though there maybe some fluid matter, yet it is so thin and subtile ; and there is so little of that in respect of the
The Universe. i25
great masses that move m those spaces, that it is as much as nothing.
These masses of matter are, either lu- minous, or opaque or dark.
Luminous bodies, are such as give light of themselves ; and such are the sun, and the fixed stars.
Dark or opaque bodies, are such as emit no light of themselves, though they are capable of reflecting it, when it is cast upon them from other bodies : and such are the planets.
There are some opaque bodies, as for instance the comets, which besides the light, that they may have from the sun, seem to shine with a "light that is nothing else but an accension, which they receive from the sun, in their near approaches to It, in their respective revolutions.
The fixed stars are so called, because; they always keep the same distance one from another.
On a view of the visible system of na- ture, by us called the universe, the grand- est and most admired object is the great luminary of day. Its splendour, its heat, its beneficial influence have always
26 The Universe.
excited the particular attention of the hu- man species, and have obtained the ado- ration of all those nations which have not been blessed with revelation.
Those who are not accustomed to as- tronomical calculation, will be surprized at the real magnitude of this luminary ; \vhich, on account of its distance from us, appears to the eye not much larger than the moon, which is only an attendant on our earth. When looking at the sun, we are viewing a globe, whose diameter is 890,000 English miles ; whereas the earth is no more in diameter than 7,97O miles : so that the sun is about 1,392,500 times bigger than the earth. Thus as it is the fountain of light and heat to all the planets, so it also far surpasses them in its bulk.
. The sun has several spots, which are visible on its surface. These spots were entirely unknown before the invention of telescopes, though they are sometimes of sufficient magnitude to be discerned by the naked eye. There is a great variety in their magnitudes ; some have been so large, as by computation to be capable of covering the continents of Asia and Af*
The Universe. 27
rica ; nay, the whole surface of the earth, or even five times its surface.
The nature and formation of the solar spots have been the subject of much speculation and conjecture. The latest observations on them, and on the nature and construction of the sun, are those of Dr. Herschel : he considers the sun as a most magnificent habitable globe, sur- rounded by a double set of clouds. Those which are nearest its opaque body, are less bright, and more closely connected together than those of the upper stratum, which form the luminous apparent globe nve behold. This luminous external mat- ter is of a phosphoric nature, havingseve- ral accidental openings in it, through V/hich we see the sun's body, or the more opaque clouds beneath. Those openings form the spots we see.
Next to the sun, the moon is the most splendid and shining globe in the hea* %-ens ; and by dissipating, in seme meas- ure, the darkness and the horrors of the night ; subdividing the year into months, and regulating the flux and reflux of the sea, she not only becojnes a pleasing, but
28 The Universes
a welcome object ; affording much for speculation to the contemplative mind, and of real use to the navigator, the traveller, and the husbandman. The Hebrews, the Greeks, the Romans, and in general, all the ancients, used to assem- ble at the time of the new moon, to dis- charge the duties of piety and gratitude for its manifold uses.
When we view this attendant on our earth in its nightly course, we seldom form an adequate idea either of its mag- nitude, or its motion. While it seems to take some hours in getting half a yard from a star which it touched, we never reflect that this is an immense mass of matter, of 218O miles in diameter, dri- ving through the heavens at the rate of considerably more than two thousand miles an hour, which is more than double of that with which a ball is shot off from the mouth of a cannon.
The face of the moon is greatly diver- sified with inequalities, and parts of dif- ferent colours, some brighter, and some darker than the other parts of her disk. When viewed through a telescope, her face is evidently diversified with hills and valleys : and the same is also shewn by
The Universe. .29
the edge or border of the moon appearing jagged, when so viewed, especially about the confines of the illuminated part when, the moon is either horned or gibbous.
M. Schroeter, of the Royal Society o£ Gottingen, in the year 1792, seems to have taken great pains to investigate the truth of this matter, i According to him, the surface of the moon appears to be much more unequal than that of our earth ; and these inequalities have great variety both in form and magnitude. There are large irregular plains, on which are observed long and narrow strata of hiljis running in a serpentine direction : some of the moun- tains form extensive chains ; others, which are in general the highest, stand alone, and are of a conical shape : some have craters ; others form a circular ring in- closing a plain. The most lofty moun- tain on the surface of our globe is suppo- sed to be Chimboraco, which is not twen- ty thousand feet in height : but there are many in the moon which are much high- er ; that which is distinguished by the name of Leibnitz^ is not less than 253OOO feet.
C
30' The Universe.
The craters of the moon are circular, and surrounded with an annular bank of hills : they are remarkable for their width, many of them being from four to fifteen geographical miles in diameter : some are not deeper than the level of the moon's surface ; others are 9000, 12,000, and 15,000 feet in depth ; that of one which M. Schroeter calls Bernoiiilli, is above 18,000 feet.
On the face of the moon are likewise volcanoes \vhich appear to the observer as lighted coals, and illuminate the neigh- bouring mountains.
With respect to the nature and con- ' struction of the moon and the probability of its being inhabited, Dr. Herschel, in his papers published in the Philosophical Transactions of 1795, concludes, after tracing the great similarity between it and the earth, as follows : u There seems on- ly to be wanting, in order to complete the analogy, that it should be inhabited.- To this it may be objected, that we per- ceive no large seas in the moon ; that its atmosphere (the existence of which has even been doubted by many) is extreme- ly rare, and unfit for the purposes of ani*
'The Universe* 31
mal life ; that its climates, its seasons, and the length of its days, totally differ from ours ; that without dense clouds (which the moon has not) there can be no rain ; perhaps no rivers, no lakes. In short, thatr notwithstanding the similarity which has been pointed out, there seems to be a decided difference in the two pla- nets we have compared. My answer to this will be, that that very difference which is now objected will rather strength- en the force of my argument than lessen its value ; we find, even upon our globe, that there is the most striking difference in the situation of the creatures that live upon it. While man walks upon the ground, the birds fly in the air, and fishes .swim in water ; we can certainly not ob- ject to the conveniences afforded by the moon, if those that are to inhabit its re- gions are fitted to their conditions as well as we on this globe are to ours. An ab- solute or total sameness seerns rather to denote imperfections, such as nature ne- ver exposes to our view ; and, on this ac- count, I believe the analogies that have been mentioned fully sufficient to estab- lish the high probability of the moon's being inhabited like the earth."
32 The Universe.
— Lastly of the earth on which we dwell, Speck as this may appear in the im- mensity of creation, it is nevertheless to us of the highest importance; we only wish to obtain a knowledge of other pla- ne ts%and systems, that we may find out their relation to this, and from thence learn our connection with the universe at large.
The external part of the earth either exhibits inequalities, as mountains and valleys ; or it is plane and level ; or dug in channels, fissures, beds, &c. for rivers, lakes, seas, &c. — These inequalities in the face of the globe most naturalists suppose have arisen from a rupture or subversion of the earth, by the force ei- ther of the subterraneous fires or waters. The earth in its natural and original state, It has been supposed by Des Cartes, and after him Burnet, Steno, Woodward, Whiston and others, was perfectly round, smooth, and equable ; and they account for its present rude and irregular form, principally from the great deluge ; but from whatever cause those inequalities may have arose, or at what period, they seem a necessary part of the econonr
The Universe* SS
nature. It is the intermediate space be- tween the mountain's top and the sea- shore that forms the habitation of plants and animals. — While there is sea-shore and high ground, there is that which is required in the system of the world ; take that away, and there would remain an aqueous globe in which the world would perish.
What the internal or central part of the earth is composed of is utterly unknown to us, though many opinions have been formed respecting it ; the utmost depth to which it hath been penetrated by human art not being more than 2400 feet, or less than half a mile, which, when compared with the length of the diameter, is a very -short distance indeed.. From its mean density, however, which is to that of wa- ter as 9 to 2, and to common stone as 9 to 5, it is presumed that it contains great quantities of metals.
The figure of the earth is that of a spheroid, having its equatorial diameter longer than its polar diameter. It is con- sequently flattest at the poles, and more protuberant at the equator.
With respect to the magnitude of the C2
34 The Universe.
earth, this has been variously determined by different authors, both ancient and modern. — The following dimensions may be taken as near the truth.
The circumference . . 25,OOO miles. The polar diameter . . 7893 miles, The equatorial diameter 7928 miles, The superficies 198,944,206 sq. miles. The solidity 263,930,000,000 cubic m. Also the seas, and unknown parts of the earth, by a measurement of the best maps, contain 160,522,026 square miles ; the in- habited parts, 38,922,180 ; of which Eu- rope contains 4,456,065 ; Asia, 10,768,- 823 ; Africa, 9,654,807 ; and America, 14,110,874 square miles.
Of the divisions of the Earth. — In tak- ing a view of the terraqueous globe the 3iiost obvious divisions that present them- selves, are those that are sketched by the yielding water on the crooked shore, call- ed continents, islands, seas, &c.
A continent is a large tract of land not separated by the sea ; as Europe, Asia, &c. An ocean is a vast collection of wa- ter not separated by land ; as the Atlan- tic, Pacific, &c. — A sea is a smaller col- lection of water communicating with the
The Universe. 35
ocean ; as the Mediterranean, the Baltic.
An island is a tract of land surrounded by water; as Great Britain, Ireland, &cc. A lake is water surrounded by land ; as the Lake of Geneva.
A cape or promontory is a point of land running far into the sea ; as the Cape of Good Hope. A bay is a part of the ocean running far into the land j as the Bay of Biscay.
A peninsula is land almost surrounded with water ; as the Morea. A gulph is a part of the sea almost surrounded with land ; as the Gulph of Venice.
An isthmus is the narrow part of land which joins the peninsula to any country ; as the Isthmus of Suez. A Strait is a nar- row passage from one sea to another ; as the Strait of Gibraltar.
The earth is also divided into four quar- ters ; Europe, Asia, Africa, and America.
Besides these, there are other divi- sions of a more varying character ; such are the political boundaries that separate kingdoms and empires.
Kingdoms, provinces, towns, &c. are divisions of the earth that change with th$
36 The Universe,
affairs of the nations that have made them ; and accordingly in different ages? :they alter their appearances.
Solar System*
CHAP. III.
Of the Solar System.
OUR solar system consists of the sun, and the planets, and comets moving about it.
The planets are bodies which appear to us like stars ; not that they are lumi- nous bodies, that is, have light in them- selves ; but they shine by reflecting the sun.
They are called planets from a Greek word, which signifies wandering ; be- cause they change their places, and do not always keep the same distance with one another, nor with the fixed stars, as the fixed stars do.
There are two kinds of planets, prima- ry and secondary. The first move round the sun, and respect him only as the cen- ter of their motions. The secondary planets, called also satellites, or moons, are smaller planets, revolving round the
S3 Solar System.
primary, while they, with the primary planets about which they move, are car- ried round the sun. The planets move round the sun at various distances, some being much nearer to him than our earth, and others being much further off.
There are nine primary planets, which are situated with respect to their distan- ces from the sun as follows :
? ? © <?
Mercury, Venus, The Earth, Mars, Ceres, Pallas t
2f " T? $
Jupiter, Saturn, and Herschel, or the Georgium Sidus.
Of these, our earth is accompanied by one moon, Jupiter has four moons, Sa- turn has seven moons, and the Georgium, planet has six moons. None of these moons, except our own, can be seen with- out a good telescope. The other five planets do not appear to have any satel- lites or moons.
All the planets move round the sun from west to east, and in the same direc- tion do the moons revolve round their primaries, excepting thos^ of the Georgi- um planet, which seem to move in a con- trary direction. The paths in which they move round are called their orbits*
Solar System. * 3$
They perform their revolutions also in very different periods of time. The time of performing their revolutions round the sun is called their year, and the time of performing their revolutions on their axes their daij.
The axis of a planet is an imaginary line conceived to be drawn through its center, about which it revolves as if on a real axis. The extremities of this linet terminating in opposite points of the planet's surface are called its poles. A bowl whirled from one's hand into the open air turns round such a line with- in itself, whilst it moves forward; and such are the lines we mean when we speak of the axes of the heavenly bodies,
Venus and Mercury being nearer to the sun than our earth, are called inferior planets, and all the rest, which are with- out the earth's orbit, are called superior planets.
The sun is placed near the common center, or rather in the lower* focus of
* If a thread be tied loosely round two pins stuck in a table, and moderately stretched by the point of a black-lead pencil carried round by an even motion and light pressure of the hand, an
40 Solar System*
the orbits of all the planets and comets, and turns round his axis in 25 days 6 hours, as is evident by the motion of spots seen on his surface. By the vari- ous attractions of the circumvolving plan- ets, he is agitated by a small motion round the center of gravity of the system. Let us suppose the earth's orbit to be a thin, even, solid plane ; cutting the sun through the center, and extended out as far as the starry heavens, where it will mark the great circle called the Ecliptic. This circle we suppose to be divided into 12 equal parts, called Signs ; each sign into 30 equal parts, called Degrees ; each degree into 6O equal parts called Minutes ; and every minute into GO equal parts, called Seconds ; so that a second is the 60th part of a minute ; a minute the 60th part of a degree ; and a degree the 360th part of a circle, or 30th part of a Sign. The ^lanes of the orbits of all the other
ova! ellipsis will be described ; the two points where the pins are fixed being1 called the foci or focuses thereof. The orbits of all the planets are elliptical, and the sun is placed in or near one of the foci of each of them ; and that in which he is placed is called the lower focus.
Solar System* 41
planets likewise cut the sun in halves ; but extended to the heavens, form circles different from one another, and from the ecliptic ; one half of each being on the north side, and the other on the south side of it. Consequently the orbit of each planet crosses the ecliptic in two op- posite points, which are called the plan- et's Nodes.
Mercury is the first planet in the or- der of the system. It is computed to be about 37,000,000 miles distant from the sun, and to move at the rate of 105,000 miles an hour, completing its orbit in about 88 of our days, or little less than three months, which is the length of its year. It is not much larger than the moon, being about 3200 miles in diame- ter.
Venus is the second planet from the sun, remarkable for its brightness, it is computed to be 68,000,000 miles from it, and to move round it at the rate of 76,000 miles an hour, completing its annual revolution in 224 days 17 hours, or above 7£ months. Its diameter is 7700 miles, and its diurnal revolution is performed in 23 hours 22 minutes. D
42 Solar System.
When it is to the west of the sun, it is a morning star ; when to the east, it is an evening star.
Our Earth is the third planet in the order of our system. Its diameter is 7970 miles, and it turns round on its axis in the course of a day. Its distance from the sun is 95,000,000 miles, and moves at the rate of 58,000 miles an hour, com- pleting its orbit in the course of a year.
Mars is the fourth planet from the sun, from which it is distant about 144,000,000 miles. It moves at the rate of 55,000 miles an hour, and completes its orbit in a little less than two of our years. Its diameter is 4200 miles, and its rotation on its axis is performed in about 24 hours and 39 minutes.
Ceres Ferdinandea is the fifth planet from the sun. Its diameter is 16O miles, and its distance from the sun is 260,000,000 miles. It was discovered on the first day of the present century by Mr. Piazzi, an Italian astronomer.
Pallas is the sixth planet in the order of the system. It was discovered by Dr. Gibers of Bremen, on the 28ch of March, 1802. Its distance from the sun
Solar System* 43
is 266,000,000 miles, and its diameter 80 miles.
This planet and the last Dr. Herschel proposes to call asteroids, because they are so much smaller than any of the oth- er planets.
Jupiter is the seventh planet in the or- der of our system, and the largest that has yet been discovered, being nearly a thousand times as large as our earth. He is computed to be about 490,000,000 miles from the sun, to go at the rate of 29,000 miles an hour, and to be 89,000 miles in diameter. He finishes his annu- al period in eleven of our years 314 days and 12 hours, and turns round his axis in 9 hours 56 minutes ; so that his year contains 10,470 days* From this plan- et's turning so swiftly on its axis, its fi- gure is more oblate than that of the earth, being more than six thousand miles long- er in its equatorial than in its polar di- ameter ; this swiftness of its diurnal mo- tion also draws its clouds and vapours into streaks or lines over its equatorial parts, forming what is called Jupiter's belts.
Saturn is the eighth planet from the
44 Solar System.
sun, and is about 900,000,000 miles dis- tant from it ; it is carried along its orbit at the rate of 22,000 miles an hour, which it completes in 29 l of our years. Its diameter is computed to be 79,OOO miles ; its rotation on its axis has been discover- ed by Herschel to be completed in about ten hours and a quarter. There is a ring, or a broad circular arch, encompasses the body of this planet, without touching it, somewhat similar to the wooden hori- zon of an artificial globe ; only that the interior space occupied by the planet is very considerable. It is about 21,000 miles in breadth ; which is equal to its distance from Saturn on all sides. It appears like a large luminous arch in the heavens, as if it did not belong to the planet.
Herschel is the ninth planet in the or- der of our system, and is twice as far dis- tant as Saturn from the sun, and will be nearly 83 years in going round it. It is ninety times as large as the earth, and is visible to the naked eye on a clear eve- ning, if the moon be absent.
Thtrse with their moons we consider as the regular bodies of our system, so
Solar System* 45
regular indeed, that their phenomena may be pretty exactly calculated for ages. There may be other planets, which hu- man observation has not yet discovered, and which, perhaps, it never may.
All the planets move nearly in the di- rection of the ecliptic ; and that space on each side of it, which bounds their ut- most deviations, is called the Zodiac. It is a broad circle or belt in the starry heavens ; and is about 16 degrees in breadth, and the ecliptic equally divides it in two all round, so that the planets are always found amongst some of the con- tellations, which form the twelve signs of the zodiac.
The reason of their motions in curve lines, is the attraction of the sun, or their gravitations towards the sun (call it which you please ;) and an oblique or side-long impulse or motion ; the former is commonly called the centripetal force , and the latter the centrifugal force.
These two motions or tendencies, the
one always endeavouring to carry them
ma straight line from the circle they move
in, and the other endeavouring to draw
D2
46 Solar System.
them in a straight line to the sun, make that a curve line they revolve in.
From the great analogy there is be- tween the other planets and our earth it is generally supposed by astronomers that they are inhabited, and indeed we can never bring ourselves to think, that an in- finitely wise Creator should dispose of all his animals and vegetables here, leav- ing the other magnificent planets, with all their noble attendance of moons, bare and destitute of rational creatures. To suppose that he had any view to our bene- fit, in creating these moons, and giving them their motions round Jupiter, Sa- turn arid Herschel; to imagine that he intended these vast bodies for any ad- vantage to us, when he well knew that they could never be seen but by a few astronomers peeping through telescopes : and that he gave to the planets regular returns of days and nights, and different seasons to all where they would be con- venient ; but of no manner of service to us, except only what immediately regards our own planet the earth ; to imagine that he did all this on our account, would be charging him impiously with having
Solar System. 47
done much in vain ; and as absurd, as to imagine that he has created a little sun and a planetary system within the shell of our earth, and intended them for our use. These considerations amount to little less than a positive proof, that all the planets are inhabited ; for if they are not, why all this care in furnishing them with so many moons, to supply those with light which are at the greater dis- tances from the sun ? Do we not see, that the farther a planet is from the sun, the greater apparatus it has for that pur- pose ? save only Mars, which being but a small planet, may have moons too small to be seen by us. We know that the earth goes round the sun, and turns round its own axis, to produce the vicis- situdes of summer and winter by the former, and of day and night by the latter motion, for the benefit of its inhabitants. IVIay we not then fairly conclude, by pa- rity of reason, that the end and design of all the other planets is the same ? and is not this agreeable to the beautiful harmo- ny which exists throughout th^ universe? Surely it is ; and raises in us the most magnificent ideas of the Supreme Being,
48 Solar System.
who is everywhere, and at all times pre- sent ; displaying his power, wisdom and goodness among all his creatures ! and distributing happiness to innumerable ranks of various beings !
Of Comets. — Of all the celestial bodies, comets have given rise to the greatest number of speculations and conjectures. Their strange appearance has in all ages been a matter of terror to the uninform- ed, who have generally looked upon them to be evil omens, and forerunners of war, pestilence, &c.
The existence of an universal connec- tion between all parts of the siderial hea- vens is now generally admitted. Comets undoubtedly form a part of this great chain ; but of the part they occupy, and of the uses for which they exist, we are in a great measure ignorant. It is a por- tion of science whose perfection is reser- ved for some distant day, when these bo- dies, and their vast orbits, may, by long and accurate observation, be added to the known parts of the solar system ; when astronomy will appear with new lights, after all our discoveries, great as we at
Solar System. 49
present imagine them to be. Upon the whole, the astronomy of comets is very imperfect ; for but little can be known with certainty where but little can be seen. Comets afford few observations, on which to ground conjecture, and are for the greatest part of their course be- yond the reach of human vision.
Like the planets, they are observed to be opaque bodies, shining only by the in- fluence of the sun, and like them are car- ried along in their orbits, by the combi- nation of the centripetal and centrifugal forces ; sometimes seeming to go for- wards, sometimes backwards, and some times to be stationary. The great eccen- tricity of their orbits make them liable to suffer considerable alterations, from the attraction of the planets, and of each oth- er.
They are called comets, from their having a long tail, somewhat resembling the appearance of hair. This, however, is not always the case ; for some comets have appeared, which were as well defi- ned, and as round as planets ; but in gen- eral, they have luminous matter diffused around them, or projecting out from them.
50 Solar System.
From the beginning of our era to this time, it is probable, according to the best accounts, that there have appeared about 500 comets. Before that time about 10O others are recorded to have been seen, but it is probable, that not above half of them were comets. And, when we con- sider, that many others may not have been perceived, from being too near the sun, from appearing in moonlight, from being in the other hemisphere, from be- ing too small to be perceived, or which may not have been recorded, we might imagine the whole number to be consid- erablv greater : but it is likely, that of the comets which are recorded to have been seen, the same may have appeared seve- ral times, and therefore the number may be less than is here stated.
Of the Moon. — The moon goes round the earth from change to change in 29 days 12 hours and 44 minutes ; and round the sun with it every year. The moon's diameter is 2180 miles; and her dis- tance from the earth's center 24O,OOO miles. She goes round her orbit in 27 days 7 hours 43 minutes, moving about
Solar System. 51
r2290 miles every hour ; and turns round her axis exactly in the time that she goes round the earth, which is the reason of her keeping always the same side towards us, and that her day and night taken to- gether is as long as our lunar month.
The moon is an opaque globe like the earth, and shines only by reflecting the light of the Sun ; therefore whilst that half of her which is towards the sun is enlightened, the other half must be dark and invisible. Hence she is incessantly varying her appearance ; sometimes she looks full upon us, and her visage is all lustre ; sometimes she shews only half her enlightened face, soon she appears as a radiant crescent, in a little time all her brightness vanishes, and she becomes a beamless orb. The full moon, or oppo- sition, is that state in which her whole disk is enlightened, and we see it all bright, and of a circular figure. The new moon is when she is in conjunction with the sun ; in this state, the whole surface turned towards us is dark, and is therefore invisible to us. The first quar- ter of the moon she appears in the form of a semicircle, whose circumference is
52 . Solar System.
turned towards the west. At the last quarter she appears again under the form of a semicircle, but with the circumfer- ence turned towards the east. These phases may be illustrated in a very plea- sing manner, by exposing an ivory ball to the sun, in a variety of positions, by which it may present a greater or small- *er part of its illuminated surface to the observer. If it be held nearly in opposi- tion, so that the eye of the observer be almost immediately between it and the sun, the greatest part of th^; enlightened side will be seen ; but if it be moved in a circular orbit, towards the sun, the visi- ble enlightened pari will gradually de- crease, and at last disappear, when the ball is held directly towards the sun. Or to apply the experiment more immedi^ ately to our purpose ; if the ball, at any time when the sun and moon are both visible, be held directly between the eye of the observer and the moon, that part of the ball on which the sun shines, will appear exactly of the same figure as the moon itself.
The moon has scarce any difference of seasons ; her axis being almost perpenv
Solar System. 53
dicular to the ecliptic. What is very singular, one half of her has no darkness at all ; the earth constantly affording it a strong light in the sun's absence ; while the other half has a fortnight's darkness and a fortnight's light by turns.
Our earth is a moon to the moon, wax- ing and waning regularly, but appearing thirteen times as big, and affording her thirteen times as much light, as she does to us. When she changes to us, the earth appears full to her ; and when she is in her first quarter to us, the earth is in its third quarter to her ; and v ice versa.
Of Eclipses. — When any of the hea- venly bodies is obscured or darkened by the shadow of another falling upon it, or by the interposition of any body, it is said to be eclipsed.
An eclipse of the moon is, when the earth, being between the sun and the moon, hinders the light of the sun from falling upon and being reflected by the moon. If the light of the sun is kept off from the whole body of the moon, it is a total eclipse j if from a part only, it is a partial one.
E
y4t Solar System.
An eclipse of the swi is, when the moon, being between the sun and the earth, hinders the light of the sun from coming to us. If the moon hides from, us the whole body of the sun, it is a to- tal eclipse, if not, a partial one.
The eclipses of the sun and the moon, though expressed by the same word, are in nature very different ; the sun, in re- ality, loses nothing of its native lustre in the greatest eclipses, but is all the while incessantly sending forth streams of light every way around him, as copiously as before. Some of these streams are, how- ever, intercepted, in their way towards our earth, by the moon coming between the earth and the sun ; and the moon ha- ving no light of her own, and receiving none from the sun on that half of the globe which is towards our eye, must appear dark, and make so much of the sun's disk appear so, as is hid from us by her interposition. What is called an eclipse of the sun, is therefore, in reality, an eclipse of the earth, which is deprived of the sun's light, by the moon's coming between, and casting a shadow upon it. The earth being a globe, only that half
Solar System. 55'
®F it, which at any time is turned towards the sun, can be enlightened by him at that time : it is some part of this enlight- ened half of the earth that the moon's shadow falls on in a solar eclipse.
In any year the number of eclipses of both luminaries cannot be less than two,, nor more than six* Eclipses of the sun are more frequent than of the moon, be- cause the sun's ecliptic limits are greater than the moon's ; yet we have more visi- ble eclipses of the moon than of the sun, because eclipses of the moon are seen from all parts of that hemisphere of the earth which isnext them, and are equally great to each of those parts ; but the sun's eclipses are visible only to that small portion of the hemisphere where the moon's shadow falls.
An eclipse of the moon can never hap- pen but at the time of full moon.
An eclipse of the sun always begins on the western, and ends on the eastern side ; because the moon, moving in her orbit from west to east, necessarily first ar- rives and touches the sun's western limb, and goes off at the eastern ; that of the
5"6 Solar System.
moon commences at the eastern and ends at the western.
The Satellites, or moons, are often eclipsed by the planets to which they be- long.
A digit is the 12th part of the sun or moon's diameter, and is a term often used in speaking of eclipses. The disk of the sun or moon is its round face, which, on account of the great distance of the object, appears fiat. The edge or border of the disk is called the limb.
The immersion of a heavenly body, is the time when an eclipse begins ; its -emersion is when it begins to re-appear.
Fixed Stars. 57
CHAP. IV. Of the Fixed Stars,
NO part of the universe affords such exalted ideas of the structure and mag- nificence of the heavens, as the consider- ation of the number, magnitude, nature, and distance of the fixed stars. We ad- mire indeed, with propriety, the vast bulk of our own globe ; but, when we consider how much it is surpassed by most of the heavenly bodies, what a point it degenerates into, and how little more even the vast orbit in which it revolves would appear, when seen from some of the fixed stars, we begin to conceive more just ideas of the extent, of the universe, and of the infinity of creation.
The fixed stars comprehend all the ce- lestial objects, excepting the sun, the moon, and the planets, and some comets which now and then appear, E2
58 fixed Star, s.
The stars, on account of their apparent- ly various magnitudes,have been distribu- ted into several classes or orders. Those which appear largest, are called stars of the first magnitude ; the next to them in lustre, stars of the second magnitude; and soon to the sixth, which are the smallest that are visible to the bare eye. This distribution having been made long be- fore the invention of telescopes, the stars which cannot be seen without the assist- ance of these instruments, are distinguish- ed by the name of telescopic stars.
They are likewise distinguished, with regard to their situation, into asterisms, or constellations ; which are nothing but assemblages of several neighbouring stars considered as constituting some deter- minate figure, as of an animal, &c. from which it is therefore denominated.
The number of constellations in the northern hemisphere is 35 ; in the south- ern 32 ; and in the ecliptic 12. Those stars which are not : in the con-
stellations, are called unformed stars ; those clusters of stars which are so dis- tant as not to be distinctly seen, are, from their cloudy appearance, comprised ua-
Fixed Stars. 59
der the name of nebulce ; and that light- coloured irregular circle or band which encompasses the heavens, and is distin- guishable from the etherial blue by its brilliancy ; that shining zone, which owes its splendour to the innumerable stars of which it is formed, and which passes through many of the constellations in its ample range, is called the Galaxy^ the via lactea, or the milky way.
The idea of classing the stars under well known forms probably originated with the Egyptian shepherds, who dur- ing the silent watches of the night (as they slept in the open air) had no other objects to contemplate than those which the starry heavens presented ; among these, assisted by the powers of a fertile imagination, they discovered a distant resemblance of such things as they were most familiar with. The shepherds thus conceiving the figures of things in the firmament, the poets embellished the il- lusion with the fictions of mythology, till the heavens were, as it were, filled with these imaginary creatures, and these were increased in after ages, and served astronomers in their accounts of the star-
60 Fixed Stars.
ry heavens, as the present divisions of the earth help geographers in the descrip- tion of the globe.
The twelve constellations which sur- round the ecliptic, commonly called the twelve signs of the zodiac, are the fol- lowing— Aries the Ram, Taurus the Bull, Gemini the Twins, Cancer the Crab, Leo the Lion, Virgo the Virgin, Libra the Balance, Scorpio the Scorpion, Sagittar- rius the Archer, Capricornus the Goat, Aquarius the Water-bearer, and Pisces the Fishes ; and they are noted on globes, &c. in the following manner : — Aries. Taurus. Gemini, Cancer. Leo. Virgo. — Libra.
T 8 n © SI ?>% =*=
Scorpio. Saggitturrius. Capricornus. Aquarius. Pisrts. Til $ V? X
The former six are called northern, and the latter southern signs ; because the former possess that half of the ecliptic which lies to the northward of the equi- noctial ; and the latter that which lies to the southward. The northern are our summer signs, the southern our winter ones.
As these twelve signs answer to the twelve months in the year, it is a very
Fixed Stars. 61
probable conjecture that the figures un- der which they are represented are de- scriptive of the seasons of the year, 01* months, in the sun's path ; thus, the first sign Aries, denotes, that, about the time when the sun enters that part of the ecliptic, the lambs begin to follow the sheep ; that on the Sun's approach to the second constellation, Taurus the Bull, is about the time of the cows bringing forth their young. The third sign, now Ge- mini, was originally two kids, and signi- fied the time of the goats bringing forth their young, which are usually two at a birth, while the former, the sheep and cow, commonly produce only one. The fourth sign, Cancer, the Crab, an animal that goes side-ways and backwards, was placed at the northern solstice, the point where the sun begins to return back again from the north to the southward. The fifth sign, Leo, the Lion, as being a very furious animal, was thought to denote the heat and fury of the burning sun, \vhen he has left Cancer, and entered the next sign Leo. The succeeding constellation, the sixth in order, received the sun at the time of ripening corn and approaching
62 Fixed Stars.
harvest ; which was aptly expressed by one of the female reapers, with an ear of corn in her hand, viz. Virgo, the Maid. The ancients gave to the next sign, Scor- pio, two of the twelve divisions of the zodiac ; autumn, which affords fruits in great abundance, affords the means and causes of diseases, and the succeeding time is the most unhealthy of the year ; expressed by this venomous animal, here spreading out its long claws into one sign, as threatening mischief, and in the other brandishing his tail to denote the comple- tion of it. The fall of the leaf was the season of the ancient hunting ; for which reason the stars which marked the sun's place at this season, into the constellation Sagittary, a huntsman with his arrows and his club, the weapon of destruction for the large creatures he pursued. The reason of the Wild Goat's being chosen to mark the southern solstice, when the suti has attained his extreme limit that way, and begins to return and mount again to the northward, is obvious enough ; the character of that animal being that it is mostly climbing, and ascending some mountain, as it browses. There yet re-
Fixed Stars. 63
main two of the signs of the zodiac to be considered with regard to their origin, viz. Aquarius and Pisces. As to the former, it is to be considered that the win- ter is a wet and uncomfortable season ; this therefore was expressed by Aquari- us, the figure of a man pouring out water from an urn. The last of the zodiacal constellations was Pisces, a couple of fishes tied together, that had been caught; the lesson was, The severe season is over ; your flocks do not yet yield then- store, but the seas and rivers are open, and there you may take fish in abun- dance.
With respect to the distances of the fixed stars, they are so extremely remote, that we have no distances in the planeta- ry system to compare to them.
The distance of the star Draconis (a star of the fifth magnitude) appears, by Dr. Bradley's observations, to be at least 400,000 times that of the sun, and the distance of the nearest fixed star not less than 40,000 diameters of the earth's an- nual orbit ; that is, the distance from the earth, of the former at least 38,000,000,- 000,000 miles, and the latter not less than
64- Fixed Stars.
7,600,000,000,000 miles. As these dis- tances are immensely great, it may both be amusing, and help to a clearer and more familiar idea, to compare them with the velocity of some moving body, bj which they may be measured.
The swiftest motion we know of, is that of light, which passes from the sun to the earth in about eight minutes ; and yet this would be above six years travers- ing the first space, and near a year and a quarter in passing from the nearest fixed star to the earth. But a cannon-ball, moving on a medium at the rate of about twenty miles in a minute, would be 3,800,000 years in passing from Draco- nis to the earth, and 760,000 years pass- ing from the nearest fixed star. Sound, which moves at the rate of about thir- teen miles in a min. would be 5,60O,OOO years traversing the former distance, and 1,128,000 in passing through the latter. The celebrated Kuygens pursued specu- lations of this kind so far, as to believe it not impossible, that there may be stars at such inconceivable distances, that their light has not yet reached the earth sincp the creation.
Fixed Stars. 65
Though the number of the stars ap- pears to be immensely great ; yet have astronomers long since ascertained the number of such as are visible to the eye, which are much fewer thaii at first sight could be imagined. Of the 3000 contained in Flamstead's catalogue, there are many that are only visible through a telescope ; and a good eye scarcely ever sees more than a thousand at the same time in the clearest heaven ; the appear- ance of innumerable more, that are fre- quent in clear winter nighty, arising from our sight's being deceived by their twink- ling, and from our viewing them confu- sedly, and not reducing them to any or- der. But a good telescope, directed in- differently to almost any point of the hea- vens, discovers multitudes that are lost to the naked eye ; particularly in the milky way. And F. de Rheita affirms, that he has observed above 2000 stars in the single constellation of Orion. The same author found above 188 in the Pleiades. Galileo found eighty in the space of the belt of Orion's sword, twenty-one in the nebulous star of his head, and above 50O in another part of him, within the com- F
66 Fixed Stars.
pass of one or two degrees of space, and more than forty in the nebulous star Prsesepe, and the recent disco\7eries of Dr. Herschel have proved the fixed stars to be immense, their regions unbounded, and perhaps infinite !
As the stars, contrary to the moon and planets, shine like our sun, by their own native light, astronomers suppose that each of them is a sun, with its system of inhabited worlds revolving round it. Un- der this idea or persuasion, of how innu- merable a family do we seem to make a part ! The immensity of the universe be- comes peopled with fellow beings, and we feel an interest in what appears to be going on at distances so vast, that what we see, as in time present, we have rea- son to believe (swift, as is the progress of light, darting from the spheres) must have happ;n<, J many ages ago. Under the idea of the universe being replenish- ed with human brings, how magnificent, how awful, are tne spectacles that present themselves to the observer of the hea- vens ! The creature of a day, of a few fleeting moments, seems to obtain a glimpse of a nqw creation, a glimpse of
Fixed Stars. 67
the end of time, in the passing away of a system.
What an amazing conception, if hu- man imagination can conceive it, does this give of the works of the Creator! Thousands of thousands of suns, multi- plied without end, and ranged ail around us, at immense distances from each oth- er, attended by ten thousand times ten thousand worlds, all hung loosens it were, in boundless space, — upheld by nothing, confined by nothing, — yet preserved in their rapid course, calm, regular and har- monious, invariably keeping the paths assigned them by the sovereign Artificer.
68 The Earth considered as a Planet.
CHAP. V.
Of the Earth considered as a Planet,
THE Earth goes round the sun in 365 days 5 hours 49 minutes, from an equi- nox or solstice to the same again ; but from any fixed star to the same again, as seen from the sun, in 365 days, 6 hours and nine minutes ; the former being the length of the tropical ijear, and the latter the length of the sidereal.
The motion of the earth in common with the rest of the planets about the sun, is in the order of the signs of the zodiac ; that is, from west to east. This zone or belt, as has been mentioned, goes round the heavens ; and along the middle, of it is the ecliptic, or circle which the earth describes annually as seen from the sun ; and which the sun appears to describe as seen from the earth.
Besides this annual revolution of the earth about the sun, in the ecliptic ; the
The Earth considered as a Planet. 69
earth turns round upon its own axis in 24 hours.
The turning of the earth upon its own axis every 24 hours, whilst it moves round the sun in a year, we may conceive by the running of a howl on a bowling green ; in which not only the center of the bowl hath a progressive motion on the green ; but the bowl in its going forward, from one part of the green to another, turns round about its own axis.
The turning of the earth on its axis, makes the difference of day and night ; it being day in those parts of the earth, which are turned towards the sun ; and night in those parts which are in the shade, or turned from the sun.
The annual revolution of the earth in the ecliptic, is the cause of the different seasons, and of the several lengths of days and nights, in every part of the world, in the course of the year.
But before we enter upon the more particular illustration of the diurnal and annual motions of the earth, together with the different lengths of days and nights, and all the beautiful variety of seasons, depending on those motions, it F2
70 The Earth considered as a Planet.
may be necessary to make the reader ac- quainted with the principle circles of the globe, as they will greatly assist him in comprehending those phenomena.
This information he may attain suffi- ciently for his present purpose in a quar- ter of an hour, if he sets the ball of a ter- restrial globe before him, or looks at the figure of it, wherein these circles are drawn and named.
The Poles are the two extremities of the earth's axis ; or those points where the imaginary line, round which it per- forms its daily revolutions, meets the earth's surface ; that which is directed towards the most northern point of the heavens, being called the north pole ; and that which is directed towards tke most southern point, the south pole ; so that they are di am e trie ally opposite to each other, and always preserve the same rela- tive situation. It is also to be observed, that these two points have not been arbi- trarily assumed by geographers and as- tronomers, to answer their particular pur- poses, as they are pointed out to us by the nature and constitution of the globe, and are easily distinguished from all
/ The Earth considered as a Planet. 71
others. The nearer we approach to them, the more we find the earth becomes bar- ren and inhospitable ; so that, under the poles, the cold is so excessive, that the country must be nearly uninhabitable. Imagine now a circle to be drawn round the globe, exactly in the middle, between these two points, and this will be the Equator ; which, properly speaking, is a great circle of the earth, that separates the northern from the southern hemis- phere, and is every where at an equal dis- tance from the poles. This circle is al- so no less remarkable, on account of its situation, than the poles ; the heat being here almost as intense as the cold is there. Every place is said to have north or south latitude as it is on the northern or southern side of this great circle.
The Tropics are lesser circles parallel to the equator, and each of them is 23 1 degrees from it ; a degree in this sense being the 360th part of any great circle which divides the earth into two equal parts. The northern tropic touches the ecliptic at the beginning of Cancer, and is thence called the Tropic of Cancer ; the southern tropic, touching the ecliptic
72 The Earth considered as a Planet.
at the beginning of Capricorn, is therefore called the Tropic of Capricorn.
The Arctic Circle has the north pole for its centre, and is just as far from the north pole as the tropics are from the equator ; and the Antarctic Circle (hid by the sup- posed convexity of the figure) is just as far from the south pole, every way round , it.
The circles 12. 1. 2. 3. 4. &c. are meri- dians to all places they pass through ; and we must suppose thousands more to be drawn, because every place that is ever so little to the east or west of any other place, has a different meridian from that other place. All the meridians meet in the poles ; and whenever the sun's cen- ter is passing over any meridian, in his apparent motion round the earth, it is mid-day or noon to all places on that me- ridian. The longitude of a place is its distance east or west from the first meri- dian, reckoned in degrees, minutes, &c. upon the equator. Supposing we call London the first, it will cut the equator in two opposite points at the distance of one hundred and eighty degrees each way ; and as the equator is the boundary
The Earth considered as a Planet. 73
which separates the northern hemisphere from the southern, so this circle may be considered as the boundary which sepa- rates the eastern hemisphere from the western.
The broad space lying between the tropics, like a girdle surrounding the globe, is called the Torrid Zone, because the sun is at one time or other perpendi- cular over every part of it, and extreme- ly torrifies or heats it. The space be- tween the tropic of Cancer and arctic circle is called the North Temperate Zone; that between the tropic of Capricorn and the antarctic circle, the South Temperate Zone: from their enjoying a mean or moderate degree of heat ; and the two circular spaces bounded by the polar cir- cles are the two Frigid Zones ; so named because of the intense cold which reigns in those regions the greatest part of the year ; and they are denominated north or south, from that pole which is in the cen- ter of the one or the other of them.
Of the Seasons, £s?c. — -Nature is always grand in her designs, sublimity and sim- plicity are the striking characteristics of
74 The Earth considered as a Planet.
her workmanship. From a few simple principles she produces the most aston- ishing effects, and charms us no less by the infinite diversity of her operations, than by the skill and contrivance which are manifested in the performance of them. Of all the effects resulting from her laws none is more simple nor more pleasing to a philosophic mind than the provision that is made for the alternate succession of day and night, and the regular return of the seasons. The phe- nomena depend upon the most simple and evident principle. We have the one merely from the rotation of our globe on its axis, and the other from the inclina- of that axis to the plane of its orbit.
The axis of the earth being inclined 23-| degrees to the plane of its orbit, makes it, in moving round the sun, have sometimes one of its poles and some- times the other nearer that luminary.
The absence of the sun's light pro- duces a proportionable degree of cold ; hence the seasons are, in the northern and southern parts of the globe, distinctly marked by different degrees of heat and sold. It is this annual turning of the
The Earth considered as a Planet. 75
poles towards the sun, that occasions the very long days in the northern and south- ern parts. It is owing to the same cause, that the sun seems to rise higher in the heavens during summer than in winter ; and this alternate sinking and rising is perceptible over the whole globe.
In order to illustrate this subject let us now take a view of the earth in its an- nual course round the sun, considering' its orbit as having no inclination | and its axis as inclining 23 -| degrees from a line perpendicular to the plane of its orbit, and keeping the same oblique di- rection in all parts of its annual course ; or, as commonly termed, keeping always parallel to itself.
In Fig. 2 let S represent the sun, the four globes the earth in different parts of its orbit, receiving from its changing po- sition the varying seasons. Ns its axis, N its north pole, s its south pole. As it goes round the sun, according to the order of the signs of the zodiac, its axis Ns keeps the same obliquity, and is still par- allel to itself.
We shall commence its annual round at the first point of Libra, when the sun, as
76 The Earth considered as a Planet.
seen from the earth will appear to enter Aries. At this time, namely the 20th of March, the sun will be in the equinoctial, and all parts of the earth will be equally enlightened from pole to pole, and the days and nights equal all over the world, for every part comes into the light at six in the morning, and goes into the dark at six in the evening. As the earth passes on in the order of the signs, in about three months, viz. on the 21st of June, it will arrive at the beginning of Capricorn, and the sun, as seen from the earth, will ap- pear at the beginning of Cancer ; during which time, by the inclined position of the earth's axis, the north pole will have gra- dually advanced into the enlightened hemisphere ; so that the whole northern polar circle will be therein, while the southern pole ir> immerged in obscurity ; the northern parts of the world will enjoy long days, while they are short in the southern parts. In this situation of the earth the tropic of Cancer is in the light from five in the morning till seven at night, the parallel of London from a quarter be- fore four till a quarter after eight ; and the polar circle just touches the dark, so
The Earth considered as a Planet. 77
that the sun has only the lower half of his disk hid from the inhabitants on that cir- cle for a few minutes about midnight.
After this the days begin to shorten in the northern parts of the world, and the nights lengthen in proportion as the earth advances to the first point of Aries, at which it arrives on the 23d of September, when the sun, as seen from the earth, will appear in .Libra. On this day the sun will be in the equinoctial again, and the days and nights will again be equal all over the globe. As the earth pro- ceeds on its orbit from this point, the north pole gradually goes into the dark ; and the south pole advances into the err- lightened hemisphere ; and on the 22d of December, when the earth enters Cancer, and the sun appears at Capricorn, the north pole will be as far as it can be in the dark, which is 23-| degrees, equal to the inclination of the earth's axis from a perpendicular to its orbit : and then, the northern parts are as much in the dark as they were in the light on the 21st oijime; the winter nights being as long as the summer days, and the winter days as short as the summer nights. G
78 The Earth considered as a Planet.
Thus we see while the earth is moving from Libra through Capricorn to Aries, the north pole remains in the illuminated hemisphere, and will therefore have six months of continual day. But in the other half year, while the earth is moving from Aries through Cancer to Libra, the north pole is turned from the sun, and therefore in darkness, but the south pole is in the illuminated hemisphere. Hence it is easy to perceive, that the inhabitants of the southern hemisphere have the same vicissitudes with those of the northern, though not at the same time, it being win- ter in one hemisphere when it is summer in the other.
During this annual course of the earth there are four days in her orbit particu- larly to be remarked ; these astronomers have distinguished by the names of the solstitial and equinoctial days. The sol- stitial days are those on which the sun ap- pears most to the northward and the southward ; they are our longest and shortest days, and are called the -winter and summer solstices. The equinoctial days are those on which the sun appears in the equator, and the days are equal to
The Earth considered as a Planet. 79
the nights, which is twice in every annual revolution of the earth, and are called the autumnal and vernal equinoxes.
The earth's annual motion causes an apparent daily declination of the sun, or in other words, he appears at different dis- tances from the equator every diurnal turn of the earth on its axis. Thus, about the 22d of December, when the earth is in Cancer, the sun will be over the tropic of Capricorn ; and consequently, by the earth's rotation on its axis, the inhabitants of every part of this circle will success- ively have the sun in their zenith, or, in other words, he will be vertical to them that day at noon. About the 20th of March the earth is at Libra, and the sun will then appear in Aries ; a central solar ray will terminate upon the surface of the earth in the equator ; and therefore the sun appears to be carried round in the celestial equator, and is successively ver- tical to those who live under that circle. About the 21st of June, when the earth is in Capricorn, a central solar ray ter- minates on the surface of the earth, in the northern tropic, and for that day the sun appears to be carried round in the tro-
80 The Earth considered as a Planet,
pic of Cancer, and is vertical to those who live under that circle. About the 23d of September the earth is in Aries, and the sun in Libra, and the central so- lar ray again terminates at the equator ; consequently the sun again appears in the celestial equator, and is vertical to those who live under it.
We have seen, that, as the sun appears to move in the ecliptic, from the vernal equinox to the tropic of Cancer, it gets to the north of ths equator, or its decli- ivition towards our pole increases. There- fore, from the vernal equinox, when the days and nights are equal, till the sun comes to the tropic of Cancer, our days lengthen, and our nights shorten ; but, when the sun comes to the tropic of Can- cer, it is then in its utmost northern lim- it, and returns in the ecliptic to the equa- tor again. During this return of the sun, its declination tov/urds our pole decrea»^s, and consequently the days decrease, and rights increase, till the sun is ar- rived in die equator 'again, and is in the autumnal equinoctial point, when the (I ivs ts will ngain be equal. As the
sun moves from thence towards the tro-
The Earth considered as a Planet, 81
pic of Capricorn, it gets to the south of the equator ; or its declination towards the south pole increases. Therefore, at that time of year, our days shorten, and our nights lengthen, till the sun arrives at the tropic of Capricorn; but, when the sun is arrived there, it is then at its utmost southeren limit, and returns in the ecliptic to the equator again. Dur- ing this return, its distance from our pole lessens, and consequently the days will lengthen, as the nights will shorten, till they become equal, when the sun is come round to the vernal equinoctial point.
The earth's orbit being elliptical, and the sun constantly keeping in its lower focus, which is 1,377,000 miles from the middle point of the longer axis, the earth comes twice so much, or 2, 754,000 miles nearer the sun at one time of the year than at another: for the sun appearing under a larger angle in our winter than summer, proves that the earth must be nearer the sun in the former season than in the latter. How then does it happen that we have not the hottest weather when we are at the least distance from the sun : — The earth is above 2,000,000 of 02
82 The Earth considered as a Planet.
miles nearer to the sun in December than it is in June, and yet in June it is the middle of summer, and in December the depth of winter, which seems a paradox. To obviate this apparent contradiction* it may be observed that the eccentricity of the earth's orbit bears no greater pro- portion to the earth's mean distance from the sun than about 1 to 60, and therefore this small difference of distance cannot occasion any great variation in the heat and cold of the different seasons. But the principal cause of this difference is, that in winter the sun's rays fall so ob- liquely upon us, that any given number of them is spread over a much greater portion of the earth's surface where we live ; and therefore each point must then have fewer rays than in summer.-— Moreover, there comes a greater degree of cold in the long winter nights, than there can return of heat in so short days ; 1 on both these accounts the cold must increase. But in summer the sun's rays fall more perpendicularly upon us, and therefore com* with greater force, and in greater numbers i>.. the same place ; and by their kr.ig continuance, a much great-
The Earth considered as a Planet. 83
er degree of heat is imparted by day than can fly off by night, so that the heat, on all these accounts, will continue to in- crease.
Thus we see by what simple principles the bountiful Author of Nature has pro- vided us with such a pleasing succession of scenes, — summer, winter, spring, and autumn, lead us* insensibly through the varied circle of the year ; and are no less pleasing to the mind, than necessary to- wards bringing to maturity the various productions of the earth. Whether the sun flames in the solstice, or pours his mild effulgence from the equator, we equally rejoice in his presence, and adore that omniscient Being who gave him his appointed course, and prescribed the bounds which he cannot pass.
by the daily motion of the earth the rising sun comes within 18 degrees of the horizon, we perceive a faint light begin to appear, which increases, and the magnificent theatre oi the universe opens gradually to our view — being fully risen, he rides in all his brightness through the vault of heaven, and approaches the west-
84 The Earth considered as a Planet.
era boundary of our sight, when the light begins to decrease, and gradually dimin- ishes till he is 18 degrees below the hori- zon, when dark night commences. This intermediate light is called the crepuscu- lum, or the morning and evening twilight.
As the sun enlightens only one half of the earth at once as it turns round its axis, he rises to some places at the same moments of absolute time when he sets to others ; and when it is mid-day to some places, it is mid-night to others.
To every place 15 degrees eastward from any given meridian, it is noon an hour sooner than on that meridian ; be- cause their meridian comes to the sun an hour sooner ; and to all places 15 de- grees westward, it is noon an hour later because their meridian comes an hour later to the sun, and so on : every 15 de- grees of motion causing an hour's differ ence of time. Therefore they who have noon an hour later than we, have their meridian, that is, their longitude, 15 de- grees westward from us : and they who have noon an hour sooner than we, have their meridian 15 degrees eastward from ours ; and so for every hour's difference
The Earth considered as a Planet. 85
of time 15 degrees difference of longi- tude. Consequently, if the beginning or ending of a lunar eclipse be observed, suppose at London, to be exactly at mid- night, and in some other place at 11 at night, that place is 15 degrees westward from the meridian of London ; if the same eclipse be observed at one in the morn- ing at another place, that place is 15 de- grees eastward from the said meridian.
Of the Precession of the Equinoxes, &?c. — Beside the changes in the length ol the days already described in the different seasons, there is another sort of change, not so obviously noticeable. The day and night together, or, in general, 24 hours, form the natural or solar day ; and this period of time also varies in its length. The inequality of the solar day is produced by two causes, either o£ which singly would yield the effect ; these are the obliquity of the ecliptic, and the earth's unequal motion therein. The earth's motion on its axis being uniform and equal at all times of the year, its days would be equal, if its orbit were a perfect circle, and its axis perpendicular to the
86 The Earth considered as a Planet.
plane of its orbit ; but the earth's annual motion in an elliptic orbit, causes the sun's apparent motion in the heavens to be un- equal. When the sun's annual motion in the heavens appears slowest, it is noon, or 12 on the sun-dial, before it is the same hour on a true-going clock ; and when quickest, it is 12 by the clock be- fore the sun be over our meridian.
Although the earth be said to complete an orbit round the sun in the course of a year, it does not return exactly to the place it set out from, neither is its cir- cuit completed exactly in a year. Adopt- ing, therefore, the apparent motion in- stead of the real ; if the sun set out as from any star, or other fixed point in the heavens, at the moment it is departing from the equinoctial, or from either tro- pic, it will come to the same equinox, or tropic again, 20 min. 17- sec. of time, or 50 sec. of a degree, before it completes its circuit round the heavens, so as to ar- rive at the same fixed star or point from whence it sets out ; for the equinoctial points recede 50 seconds of a degree west- ward every year, contrary to the sun's annual progressive motion. This is call- ed the Precession of the Equinoxes,
The Earth considered as a Planet. 87
When the sun arrives at the same equi- noctial or solstitial point, he finishes what we call the tropical year ; which, by ob- servation, is found to contain 365 days 5 hours 48 minutes 57 seconds: and when he arrives at the same fixed star again, as seen from the earth, he completes the sidereal year, which contains 365 days 6 hours 9 minutes 14~ seconds. The sidereal year is therefore 2O min- utes 17- seconds longer than the solar or tropical year, and 9 minutes 14 1 seconds longer than the Julian or civil year, which we state at 365 days 6 hours : so that the civil year is almost a meanbe- twixt the sidereal and tropical.
The anticipation of the equinoxes, and consequently of the seasons, is by no means owing to the precession of the equinoctial and solstitial points in the heavens (which can only affect the appa- rent motions, places and declinations of the fixed stars) but to the difference be- tween the civil and solar year, which is 1 1 minutes 3 seconds ; the civil year con- taining 365 days 6 hours, and the solar year 365 days 5 hours 48 minutes 57 seconds,
88 The Earth considered as a Planet.
The above 11 minutes 3 seconds, by which the civil or Julian year exceeds the solar, amounts to 11 days in 1433 years, and so much our seasons have fall- en back with respect to the days of the months, since the time of the Nicene Council in A. D. 325, and therefore in order to bring back all the fasts and fes- tivals to the days then settled, it was re- quisite to suppress 1 1 nominal days. And that the same seasons might be kept to the same times of the year for the future, to leave out the bissextile-day in February at the end of every century of years not di- visible by 4 ; reckoning them only com- mon years, as the 17th, 18th, and 19th centuries, viz. the years 1700, 1800, 1900, £cc. because a day intercalated every fourth year was too much, and retail, the bissextile-day at the end of those cen- turies of years which are divisible by 4, as the 16th, 20th, and 24th centuries ; viz. the years 1600, 2000, 2400, &c. Other- wise, in length of time, the seasons would be quite ^reversed with regard to thr months of the year ; though it would have required near 23,783 years to have brought about such a totaj change.
The Earth considered as a Planet, 89
This new form of reckoning was or- dained by Pope Gregory, and is there- fore called the Gregorian, or the new style, and has been adopted by almost all the enlightened nations of the world ; there are some, however, who still reckon according to the old style, viz. as if no alteration had been made by Pope Gre- gory.
H
9'0 Atmosphere,
CHAP. VI.
Of the Air and Atmosphere.
WE have already considered the earth as a planet, or one of the great masses of matter moving about the sun ; we shall now consider it as it is made up of its several parts, abstracting from its diur- nal and annual motions.
The exterior part of this our habitable world is the air or atmosphere ; a light, thin fluid, or springy body, that incom- passes the solid earth on all sides, and partakes of all its motions., both annual and diurnal.
The composition of that part of our atmosphere properly called air, was till lately but very little known. Formerly it was supposed to be a simple, homoge- neous, and elementary fluid. But the experiments of Dr. Priestley and others have discovered, that even the purest kind of air, which they call vita'.
Atmosphere. 91
plilogisticated, is in reality a compound, and might be artificially produced in va- rious ways. This dephlogisticated air,> however, is but a small part of the com- position of our atmosphere. By accu- rate experiments, the air we usually breathe, is composed of only one-fourth part of this dephlogisticated air, or per- haps less, the other three parts, or more, consisting of what Dr. Priestly calls phlo~ gisticated, and M. Lavoisier, in the new chemistry, mephitzc, or azotic air, which cannot be breathed, and in which ani- mals die.
Though air seems to be a kind of re- pository, wherein all the poisonous efflu- via arising from putrid and corrupted mat- ters are lodged ; yet it has a wonderful facilitv of purifying itself, and of deposi- ting those vapours contained in it ; so that it never becomes noxious except in particular places, arid for a short time ; the general mass remaining upon all oc- casions pretty much the same. The way in which this purifaction is effected is dif- ferent, according to the nature of the va- pour with which the air is loaded. That which most universally prevails is water ;
92 Atmosphere.
and from experiments it appears, that the quantity of aqueous vapour contained in the atmosphere is immense. Dr. Halley, from an experiment on the eva- poration from a fluid surface heated to the same degree with that given by our meridian sun, has calculated, that the evaporation from the Mediterranean Sea in a summer's day is 5280 millions of tons of water, which is more than it re- ceives from all the nine large rivers that empty themselves into it. Dr. Watson, in his Chemical Essays, has given an ac- count of some experiments made with a view to determine the quantity of the wa- ter raised from the "earth itself alone in time of drought. He informs us, that when there had been no rain for above a month, and the grass was become quite brown and parched, the evaporation from an acre was not less than 1600 gallons in twenty-four hours. Making afterwards two experiments, when the ground had been wetted by a thunder-shower the day before, the one gave 1973, the other 1905 gallons, in twelve hours. From this the air is every moment purified by the ascent of the vapour, which, flying off in-
Atmosphere. 93
to the clouds, thus leaves room for the exhalation of fresh quantities ; so that as the vapour is considerably lighter than the common atmosphere, and in conse- quence ascends with great velocity, the air during all this time is said to be dry, notwithstanding the vast quantity of aque- ous fluid that passes through it.
In the physical economy also, another provision is made for the continual reno- vation of the atmosphere. Plants derive subsistence from the very air that is unfit for animal life, and in return, actually emit that vital or dephlogisticated air, upon the enjoyment of which the latter depends. Thus we see a constant circulation of benefits maintained between the two great provinces of organized nature. The plant purifies what the animal has poison- ed ; in return, the contaminated air is more than ordinarily nutritious to the plant. Agitation with water appears to be another of these restoratives. The foulesi air shaken in a bottle with water for a sufficient length of time, recovers a great degree of its purity. Here, then again, allowing for the scale upon which nature works, we see the salutary effects H2
94 Atmosphere.
of storms and tempests. The yesty waves, which confound the heaven and the sea, are doing the very thing which is done in the bottle, and are a perpetual scarce of freshness to our atmosphere.
The atmosphere, as we have seen, contains a great deal of water, together with a vast heterogeneous collection of particles raised from all bodies of matter on the surface of the earth, by effluvia, ex- halations, &c. so that it may be consider- ed as a chaos ©f the particles of all sorts of matter confusedly mingled together. And hence the atmosphere has been con- sidered as a large chemical vessel, in which the matter of all kinds of subluna- ry bodies is copiously floating ; and thus exposed to the continual action of that immense surface, the sun ; from whence proceed innumerable operations, subli- mations, separations, compositions, di- gestions,fermentations, putrefactions, &c»
There is, however,one substance, nam- ly, the electrical fluid, which is very dis- tinguishable in the mass of the atmos- phere. To measure the absolute quanti- ty of this fluid, either in the atmosphere, or any other substance, is perhaps impos-
Atmosphere. 95
sible ; and all that we know on this sub- ject is that the electric fluid pervades the atmosphere ; that it appears to be more abundant in the superior than the inferior regions ; that it seems to be the imme- diate bond of connection between the at- mosphere and the water which is suspen- ded in it ; and that, by its various opera- tions, the phenomena of the meteors are occasioned.
It is the opinion of the most celebrated philosophers of the present day, that the electric fluid is no other than the light of the sun ; that it issues from that lumina- ry in the pure state of electricity, that joining the particles of our atmosphere, it becomes light, and uniting with the gros- ser earth Jire. — The evaporation of wa- ter is attended with an absorption of this fluid from the 'surface of our globe, and, on the other hand, the conversion of steam into water, is attended with a de- position of this subtle fluid ; so that there is a circulation in the electric fluid as there is in the water. It descends origin- ally from the sun ; pervades the whole srubstance of the globe ; and perspiring, as it were, at every pore, ascends beyond
96 Atmosphere.
the clouds ; and, passing the extreme boundaries of our atmosphere, returns to the sun from whence it came.
The uses of the atmosphere are so ma- ny and great, that it seems indeed abso- lutely necessary, not only to the comfort and convenience of men, but even to the existence of all animal and vegetable life, and to the very constitution of all kinds of matter whatever, and without which they would not be what they are ; for by it we live, breathe, and have our being ; and by insinuating itself into all the va- cuities of bodies, it becomes the great spring of most of the mutations here be- low, as generation,corruption,dissolution, &c. and without which none of these op- erations could be carried on. Without the atmosphere, no animal could exist, or indeed be produced; neither any plant, all vegetation ceasing without its aid ; there would be neither rain nor dews to moisten the face of the ground : and, though we might perceive the sun and stars like bright specks, we should be in utter darkness, having none of what we call day-light, or even twilight: nor would either fire or heat exist without it. In
Atmosphere. 97
short, the nature and constitution of all matter would be changed and cease; wan- ting this universal bond and constituting principle*
As to the weight and pressure of the air, it is evident that the mass of the at- mosphere, in common with all other mat- ter, must be endued with weight and pressure ; and this principle was asserted by almost all philosophers, both ancient and modern. But it was only by means of the experiments made with pumps and the barometrical tube, by Galileo and Torricelli, that we came to the proof, not only that the atmosphere is endued with a pressure, but also what the measure and quantity of that pressure is. Thus it is found, that the pressure of the atmos- phere sustains a column of quicksilver, in the tube of the barometer, of about thirty inches in height : it therefore follows, that the whole pressure of the atmosphere is equal to the weight of a column of quick silver, of an equal base, and thirty inches height: and, because a cubical inch of quicksilver is found to weigh nearly half a pound avoirdupois, therefore the whole thirty inches, or the weight of the atmosr
98 Atmosphere.
phere on every square inch of surface is equal to 15lb. Again, it has been found that the pressure of the atmosphere bal- ances, in the case of pumps, &c. a column of water of about 3 | feet high ; and the cubical foot of water weighing just 100O ounces, or 6~^.b. 34-| times 62-|, or 2158 Ib. will be the weight of the column of water, or of the atmosphere, on a base of a square foot; and consequently the 144th part of this, or 15lb. is the weight of the atmosphere on a square inch ; the same as before. Hence Mr. Cotes computed, that the pressure of this ambient fluid on the whole surface of the earth, is equiva- lent to that of a globe of lead of sixty miles in diameter. And hence also it appears, that the pressure upon the human body must be very considerable ; for as every square inch of surface sustains a pressure of 15lb. every square foot will sustain 144 times as much, or 2160lb. then, if the whole surface of a man's body be suppo- sed to contain fifteen square feet, which is pretty near the truth, he must sustain 15 times 2160, or 32400lb. that is near 14-| tons weight for his ordinary load* By this enormous pressure we should un-
Atmosphere. 98
doubtedly be crushed in a moment, if all parts of our bodies were not filled either with air or some other ela&tic fluid, the spring of which is just sufficient to coun- terbalance the weight of the atmosphere,, But, whatever this fluid may be, it is cer- tain that it is just able to counteract the weight of the atmosphere, and no more : for if any considerable pressure be super- added to that of the air, as by going into deep water ,or the like,it is always severe- ly felt, let it be ever so equable, at least when the change is made suddenly ; and if, on the other hand, the pressure of the atmosphere be taken off from any part of the human body, as the hand for instance, when put over an open receiver, from whence the air is afterwards extracted, the weight of the external atmosphere then prevails, and we imagine the hand strongly sucked down into the glass.
The difference in the weight of the air which our bodies sustain at one time more than another, is also very consider- able, from the natural changes in the state of the atmosphere. This change takes place chiefly in countries at some distance from the equator ; and, as the barometer
10O Atmosphere.
varies at times from twenty-eight to thitv ty-one inches, or about one tenth of the whole quantity, it follows, that this diffe- rence amounts to about a ton and a half on the whole body of a man, which he therefore sustains at one time more than at another. On the increase of this natu- ral weight, the weather is commonly fine, and we feel ourselves what we call braced, and more alert and active ; but, on the contrary, when the weight of the air di- minishes, the weather is bad, and people feel a listlesness and inactivity about them. And hence it is no wonder that persons suffer very much in their health, from such changes in the atmosphere es- pecially when they take place very sud- denly.
The weight of the atmosphere has great influence on a number of physical pheno- mena. It compresses all bodies, and op- poses their dilatation. It is an obstacle to the evaporation of fluids. The water of the sea is by this cause preserved in its liquid state, without which it would take the vaporous form, as we see in the vacu- um of the air pump. The pressure of the air on our bodies preserves the state
Atmosphere. 101
both of the solids and fluids ; and from the want of this due pressure it is that on the summits of lofty mountains the blood often issues from the pores of the skin, or from the lungs.
Various attempts have been made to ascertain the height to which the atmos- phere is extended all round the earth. These commenced soon after it was dis- covered by means of the Torricellian tube that air is endued with weight and pres- sure. And had notthe air an elastic pow- er, but were it every where of the same density, from the surface of the earth to the extreme limit of the atmosphere, like water, which is equally dense at all depths it would be a very easy matter to deter- mine its height from its density and the column of mercury it would counterbal- ance in the barometer tube : for, it having been observed, that the weight of the at- mosphere is equivalent to a column of thirty inches or 2-| feet of quicksilver and the density of the former to that of the latter, as 1 to 1104O; therefore the height of the uniform atmosphere would be 11040 times 2£ feet, that is, 27600 feet, or little more than 5^ miles. But the air, I
102 Atmosphere. ,
by its elastic quality, expands and con- tracts ; and it being found, by repeated experiments in most nations of Europe, that the spaces it occupies, when compres- sed by different weights, are reciprocally .proportional to the weights themselves ; or, that the more the air is pressed, so much the less space it takes up ; it follows that the air in the upper regions of the at- mosphere must grow continually more and more rare, as it ascends higher ; and indeed that, according to that law, it must necessarily be extended to an indef- inite height. At the height of 3-| miles the density of the atmosphere is nearly 2 times rarer than it is at the surface of the earth ; at the height of seven miles, 4 times rarer ; and so on, according to thr following table.
Height in miles. Number of times rarer
3* 2
7 4
14 16
21 64 N
28 256
35 1024
42 4096
' 16384
Atmosphere,, 105
56 65536
63 262144
7O 1048576
By pursuing these calculations, it might be easily shewn, that a cubic inch of the air we breathe would be so much rarefied at the height of 500 miles, that it would fill a sphere equal in diameter to the orbit of Saturn. Hence we may per- ceive how very soon the air becomes so extremely rare and light, as to be utterly imperceptible to all experience ; and that hence, if all the planets have such atmos- pheres as our earth, they will, at the dis- tances of the planets from one another, be so extremely attenuated, as to give no sensible resistance to the planets in their motion round the sun for many, perhaps hundreds or thousands of ages to come. Even at the height of about fifty miles, it is so rare as to have no sensible effect on the rays of light.
Mr. Boyle in his physico-mechanical experiments concerning the air, declares it probable that the atmosphere may be several hundred miles high ; which is easy to be admitted, when we consider^ what he proves in another part of the
104 Atmosphere.
same treatise, viz. that the air here about the surface of the earth, when the pressure is taken from it, dilates into 10,000, and even at last into 13,679 times its space ; and this altogether by its own expansive force, without the help of fire. In fact, it appears, that the air we breathe is compressed by its own \veight into at least the 13,679th part of the space it would possess in vacua. But, if the same air be condensed by art, the space it would take up when dilated, to that it possesses when condensed, will be, accor- ding to the same author's experiments, as 550.0OO to 1.
Our direct experiments, however, not reaching to any great heights into the re- gions of the atmosphere, and not know- ing how far air may be expanded, we are incapable of determining to what height the atmosphere is actually extended.
Meteors. 105
CHAP. VII.
Of the Meteors.
WE have seen that the atmosphere is a vast laboratory, in which nature ope- rates immense analyses, solutions, preci- pitations, and combinations ; it is a grand receiver, in which all the attenuated, vo- latilized productions of terrestrial bodies are received, mingled, agitated, combined and separated. Considered in this view, the atmospheric air is a chaos, an inde- terminate mixture of mineral, vegetable, and animal effluvia, which the electric fluid is pervading and traversing contin- ually. The grand changes it experiences, and of which we are sensible in ex- tensive spaces by the appearance of wa- ter, light, or noise, are called meteors* As the state of the atmosphere is ever varying, the meteors assume different forms ; some delighting us with their ap- pearance, while others wear a terrifying 12
1O6 Meteors.
aspect. In this repository is collected the gentle dew and hoar-frost ; here clouds are gathered and carried along by the wind, to refresh the earth in falling showers, give rise to rivers, spread vast inundations of water over the fields, or lay them under a covering of snow or hail ; here mock-suns, mock-moons, ha- loes, and rainbows make their gaudy but transitory appearance ; and here the wa- ter-spout, dreadful to the mariner ; here rolls the dreadful thunder, here lightnings dart their vivid flames, and sometimes, striking upon the earth, destroy its pro- ductions, fill its inhabitants with terror, and sometimes strike them dead ; here the auroras, or streamers, the ignesfatui, or wandering fires, called also Jack with the Lantern ; here falling stars, as they are ignorantly termed, or fiery balls of va- rious sizes, appear with splendour during the gloom of night, and astonish man- kind, who too often seem willing, with superstitious awe, to find portentous o- mens of dire calamities in these curious phenomena, rather than investigate their causes or discover their uses.
Meteors* 107
To account for these various appear- ances in a satisfactory manner, it is plain that we ought to have an intimate ac- quaintance with the constitution of the at- mosphere ; with the nature of those pow- erful agents by which it appears to be principally influenced, viz. fire, light, and electric fluid ; and with their peculiar modes of operation and action upon one another and upon the atmosphere, and this in every possible variety of circum- stances. Nor is even all this sufficient : the various phenomena of rain, wind, snow, thunder, heat, cold, &c. are known to depend very much upon the situation of different places on the surface of the earth ; and the occasional variations are with great reason suspected to proceed, partly at least, from changes which take place in the bowels of the earth : whence we ought not only to be perfectly well ac- quainted with geography, but with mine- ralogy also: and that to an extent at which human knowledge will probably never arrive.
In a subject so very difficult, it is not to be 'supposed that any thing like a certain and established theory can be laid down
108 Meteors.
in this little elementary work. As eva- poration, however, seems particularly to be concerned in the production of the me- teors, we shall take a view of that opera- tion of nature, the extent of which we have noticed in the preceding chapter. This process may be reckoned in a par- ticular manner the effect of heat. Upon this principle vapour is shown to be a compound of water and fire ; and such it is supposed to be by philosophers of the highest rank. In considering this opera- tion, however, as carried on by nature, we shall soon find, that it proceeds in a manner very different from what takes place in our chemical operations. In the latter, evaporation is merely the effect of heat; and the process cannot go on with- out a considerable degree of it. In the natural way, on the contrary, the process goes on under almost every degree of cold we know ; the vapours ascend to a height which has never yet been determined ; and, from the extreme cold which they sustain, show evidently that they are con- nected with our atmosphere by mrans of some other agent besides heat. From the continual ascent of vapour indeed, if the
Meteors. 109
operations of nature were of the same kind with those of art, the upper parts of our atmosphere would be always involved in a fog, by reason of the condensation of the vast quantity which continually as- cends thither : but so far is this from be- ing the case, that in those elevated regions to which the vapours continually ascend, the air is much drier than at the surface of the ground.
From many experiments, indeed, it is evident, that water, after being reduced into a state of vapour, is capable of un- dergoing a certain change, by which it lays aside its fluidity entirely, and even to appearance its specific gravity ; so that it becomes, as far as we can judge, a substance totally different from what it was before. After water has attained to this state, our inquiries concerning it must in a great measure cease ; but as it is not in the immediate product of evapo- ration that rain has its source, and as va- pours change their nature in the atmos- phere, so as to be no longer sensible to the hygrometer or to the eye, and do not be- come vapour again till clouds appear, we must acknowledge it to be very probable,
110 Meteors.
that the intermediate state of vapour is no other than air ; and that the clouds do not proceed from any distinct fluid in the at- mosphere, but from a decomposition of a part of the air itself, perfectly similar to the rest.
Granting this to be the case, and we can scarcely hope for a more probable conjecture on the subject, the decompo- sition of the vapour will be easily accoun- ted for. If by any natural process the water can be con verted into air, and if the latter is only water partially decomposed; then, by an inversion of the process, air may be instantly re-converted into water, and will become visible in fog or mist, or be condensed into rain, consisting of greater or smaller drops, according to the degree to which this inverted process is carried.
It is generally supposed by meteorolo- gists, from all the clouds, fogs, hail, rain, and snow, being electrified, that the elec- tric fluid is the agent employed in the for- mation of these meteors, and that it is this fluid which acts in the re-conversion of air into water. This process may be par- ticularly observed in the summer season,
Meteors. 1 1 1
when the horizon is suddenly overcast, and a copious torrent of rain ensues, which cannot be from the rising of any aqueous vapours at the time, but must be from a precipitation of water that existed in an invisible state in the atmosphere.
Water may therefore exist in air ; 1st, in an invisible state, which is the case when the dissolving power of air is considera- ble ; 2dly, in a state of incipient separa- tion, in which case it forms clouds, mists ^ or fogs ; 3dly, and lastly, in a state of ac- tual separation, in which case it forms ei- ther rain, properly so called, or snow, or hail.
Clouds are those well known assembla- ges of vapours that float in the atmosphere, have different degrees of opacity, which arise from their extent and density, and generally have pretty well defined boun- daries. Their height above the surface of the earth (we mean not above the moun- tains) is various, but hardly ever exceeds a mile or a mile and a half. In hot wea- ther, or hot climates, the clouds, being more rarefied, are lighter, and ascend much higher than they do in colder cli- mates, or colder weather : and indeed, in
112 Meteors.
cold weather the clouds frequently touch the very surface of the earth ; for a fog may with propriety be called a cloud close to the ground.
A mist is a very indefinite word. It means an incipient formation of clouds, or haziness ; and it often denotes a very small rain, or deposition of water in par- ticles so small as not to be visible singly.
The snow is formed when the atmos- phere is so cold as to freeze the particles of rain as soon as they are formed, and the adherence of several of those parti- cles to each other, which meet and cling to each other as they descend through the air, forms the usual fleeces of snow, which are larger, (since they are longer in descending, and have a greater oppor- tunity of meeting) when the clouds are higher than when they are lower.
The hail differs from snow in its con- sisting of much more solid, and much more dehned pieces of congealed water. It is sui posed that the water, already formed into considerable drops, is driv- en and detained a considerable time through a cold region of the atmosphere, by the wind, which almost always accom-
Meteors. 113
panics a fall of hail. But the globes of ice, or hail-stones, in a fall of hail, some- times far exceed the usual size of the 'drops of rain ; which shews that by the action of the wind, the congealed parti- cles must be forced to adhere to each oth- er ; and, in fact, though the small hail- stones are more uniformly solid and glo- bular, the large ones almost always con- sist of a harder nucleus, which is sur- rounded by a softer substance, and some- times by various distinct pieces of icet just agglutinated. Their shape is sel- dom perfectly globular.
The phenomena of dew and hoar-frost seem to proceed from a quantity of aque- ous and undecomposed vapour which always exists in the atmosphere ; and which, being raised by mere heat, is con- densed by mere cold, without undergo- ing that process by which water is chan- ged into air.
If the cold be very intense, hoar-frost appears instead of dew ; which is nothing more than the dew frozen after it falls upon the ground, in the same manner that the vapour in a warm room congeals on the inside of the windpws in a frosty night. K
Meteors.
Lightning is found to be a flash, pro- duced by the electrical fluid rush ing from? one part into another ; and thunder the sound of the rushing torrent, reverbera- ted among the clouds. The aurora bo- •realis, or northern dawn, is likewise an electrical phenomenon. It is a lambent or flashing light, seen at night in some periods more often than in others, espe- cially about the poles. The fery -balls, \vhich are seen shooting through the at- mosphere in the night, of various magni- tudes and of different forms, seem all to rise from inflammable vapours, taking lire from their fermenting, or effervescing in the air.
The Rainbotv is one of the most sur- prising of the works of God, which the Hebrews called the bow of God, and the Greeks the Daughter of Wonder. This phenomenon is seen in the falling rain or dew, and not in the cloud whence that rain or dew proceeds ; it is caused by a reflection and refraction of the sun's rays from the globular particles of rain. The face of this beautiful iris, or bow, is ting- ed with all the primogenial colours in iheir natural order; viz* violet^ indigo •,
Meteors. 115
green, yellow and red. It always appears in that part of the heavens oppo- site the sun.
The Halos, are circles somewhat akin to the rainbow, which appear about the sun and moon,and are sometimes various- ly coloured. They never appear in a rainy sky, but in a rimy and frosty one* and are formed by the refraction of the rays of light, without any reflection as in the rainbow*
Mo.ck-suns and mock-moons are repre- sentations of the face of the true sun an.d. moon by reflection in the clouds.
The weight and pressure of the atmos- pherical air have been explained in the preceding chapter. We shall now exam- ine the particulars relative to its progres- sive motion, which we denominate wind*
Wind is a stream or current of air ; as the air is a fluid, its natural state is that of rest, which it endeavours always to keep or retrieve by an universal equilibri- um of all its parts. When, therefore, this natural equilibrium of the atmosphere happens by any means to be destroyed in any part, there necessarily follows a mo-
116. Meteors*
tion of all the circumjacent air towards that part to restore it ; and this motion of the air is what we call whid.
Hence, with respect to that place where the equilibrium of the air is disturbed, we see the wind may blow from every point of the compass at the same time; and those who live northwards of that point have a north wind ; those who live southwards, a south wind ; and so of the rest : But those who live on the spot, where all these winds meet and interfere, are oppressed with turbulent and boisterous weather, whirlwinds and hurricanes ; with rain, tempest, lightning, thunder, &c.
Many are the particular causes which produce winH by interrupting the equi- poise of the atmosphere ; but the most general causes are two, viz. heat, which, by rarefying the air, makes it lighter in some places than it is in others ; and cold which, by condensing it, makes it heavier. Hence it is, that in all parts over the tor- rid zone, the air being more rarefied by 3 greater quantity of the solar rays, is much lighter than in the other parts of the atmosphere, and most of all over the equatorial parts of the earth. And since
Meteors. 117
trie parts at the equator are most rarefied which are near the sun ; and those parts are, by the earth's diurnal rotation east- ward, continually shifting to the west ; it follows, that the parts of the air which lie on the west side of the point of greatest rarefaction, and, by flowing towards it, meet it, have less motion than those parts on the east of the said point, which follow it ; and therefore the motion of the east- ern air would prevail against that of the western air, and so generate a continual east wind, if this were all the effect of that rarefaction. But we are to consider that as all the parts of the atmosphere are so greatly rarefied over the equator, and all about the poles greatly condensed by ex- treme cold, this heavier air from either pole is constantly flowing towards the equator, to restore the balance destroyed by the rarefaction and levity of the air ov- er those regions ; hence, in this respect alone, a constant north and south wind would be generated.
Now it is easy to understand, that by a
composition of these two directions of the
air from the east and north, a constant
north-east wind will be generated in the
K2
118 Meteors.
northern he mi sphere, and a constant south- east wind in the southern hemisphere, to a certain distance on each side the equa- tor, all round the earth. And this case we find to be verified in the general trade -winds) which constantly blow from the north-east and south-east, to about thirty degrees on each side the equator, where those parts are over the open ocean, and not affected with the reflection of the sun- beams from the heated surface of the land, for in this case the wind will always set in upon the land, as on the coast of Guin- ea, and other parts of the torrid zone, we know it does.
The temperature of a country with res- pect to heat or cold, is increased or dim- inished by winds, according as they come from a hotter or colder part of the world. The north and north-easterly winds, in this country and all the western parts of Europe, are reckoned cold and drying winds. They are cold because they come from the frozen region of the north pole, or over a great tract of cold land. Their drying quality is derived from their co- ming principally over land,"* and from a
* This is not true with regard to the United States ; for here the north-east wind, coming over the ocean, instead of land, brirtjjs along with it so great a degree of humidity as always
Meteors. 119
well known property of the air, namely, that warm air can dissolve, and keep dis- solved, a greater quantity of water than colder air : hence the air which comes from colder regions being heated over warmer countries, becomes a better sol- vent of moisture, and dries up with great energy the moist bodies it comes in con- tact with ; and, on the other hand, warm air coining into a colder region deposits a quantity of the water it kept in solution and occasions mists, fogs,clouds,rains,&:c. In warm countries sometimes the winds which blow over a great tract of highly heated land, become so very drying, scorching and suffocating, as to produce dreadful effects. These winds under the name ofsolanos, are often felt in the des- erts of Arabia, in the neighbourhood of the Persian gulph, in the interior of Af- rica, and in some other places. There are likewise in India, part of China, part of Africa, and else where, other winds, which deposit so much warm moisture as to sof- ten, and actually to dissolve glue, salts, and almost every article which is soluble in water.
to produce rain or snow, according to the temperature of the air ; whereas, as here stated, in Europe the same wind bio wine; over land, it always produces dry, fair weather.
120 Meteors.
It is impossible to give any adequate account of irregular winds, especially of those sudden and violent gusts which come on at very irregular periods, and generally continue for a short time. They some- times spread over an extensive tract of country, and at other times are confined within a remarkably narrow space. Their causes are by no means rightly understood though they have been vaguely attributed to peculiar rarefactions, to the combined attractions of the sun and moon, to earth- quakes, to electricity, £^c. They are called in general hurricanes, or they are the principal phenomenon of a hurricane, that is, of a violent storm.
Almost every one of those violent winds is attended with particular pheno- mena, such as droughts or heavy rains, or hail, or snow, or thunder and lightning, or several of those phenomena at once. They frequently shift suddenly from one quarter of the horizon to another, and then come again to the former point. In this case they are called tornadoes.
Iu some parts of the Indian ocean there are winds which blow one way du- ring one half of the year, and then blow the contrary way during the other half
Aleteor*. 121
of the year. These winds are called monsoons, and owe their origin to causes similar to what has been pointed out.
When the gusts of wind come from different quarters at the same time, and meet in a certain place, there the air ac- quires a circular, or rotatory, or screw- like motion, either ascending or descend- ing, as it were, round an axis, and this axis sometimes is stationary, and at other times moves on, in a particular direction. This phenomenon, which is called a whirlwind, gives a whirling motion to dust, sand, water, part of a cloud, and sometimes even to bodies of great weight and bulk ; carrying them either upwards or downwards, and lastly scatters them about in different directions.
The water-spout has been attributed principally, if not entirely, to the meeting of different winds. In that case the air in its rotation acquires a centrifugal mo- tion ; whence it endeavours to recede from the axis of the whirl, in conse- quence of which a vacuum, or, at least a considerable rarefaction of air, takes place about the axis, and, when the whirl takes place at sea, or upon water, the water ri-
122 Meteors.
ses into that rarefied place ; for the same reason which causes it to ascend in- to the exhausted tube, and forms the water-spout or pillar of water in the air. The water-spouts generally break about their middle, and the falling waters oc- casion great damage, either to ships that have the misfortune of being under them, or to the adjoining land ; for such spouts are sometimes formed on a lake, or river, or on the sea close to the land.
As the motion of the air has a greater or lesser velocity, the wind is stronger or weaker ; and it is found from observation, that the velocity of the wind is various, from the rate of 1 to 1OO miles per hour. The following particulars respecting the velocity, &?<:. of the wind are extracted from a table which appeared in the 51st volume of the Philosophical Transactions, by Mr. J. Smeaton, the celebrated engi- neer.—
When the velocity of the wind is one mile per hour it is hardly perceptible. From 2 to 3 just perceptible.
4 — 5 gentle pleasant wind, or breezes,
10 — 15 pleasant brisk gale.
20 —25 very brisk.
30 —35 high winds.
Meteors* 120
40 — 45 very high.
50 miles per hour a storm or tempest,
60 a great storm.
80 a hurrscane.
JQQ C a hurricane that tears up trees
' \ carries buildings before it, 8cc,
The winds are of immense and indis- pensable use. Besides their more ob- vious effects in driving of ships, wind- mills, &Pc. they preserve, by mixing, the necessary purity of the air. The winds, likewise drive away vapours, clouds fogs, and mists from those parts in which they are copiously formed, to others which are in want of moisture ; and thus the whole surface of the earth is supplied with water. It is the winds which diminish the heat, and augment the moisture of the torrid zone, and produce contrary effects on those of the polar re- gions, so as to render those districts of the globe, which the ancients deemed totally unfit for the abode of man, and other animals, by reason of excessive heat, not only habitable, but salutary and pleasing to man and beast, and yielding great variety and abundance of the choice productions of nature*
124 Springs ) Rivers , and the Seat,
CHAP. VIII.
Of Springs, RiverSy and the Sea.
HAVING viewed water as it takes its departure from the bosom of the deep and forms the watery meteors, we shall now survey it as it rises in the salient spring, and gives birth to the gurgling rill, or uniting, gives coolness to the land- scape in the magnificent stream, that irl its ample range fertilizes its neighbour- hood.
Various have been the theories, or rather hypotheses relating to the origin of springs ; but it seems the general o- pinion of those who have made this branch of natural philosophy their study, that the true principles which supply the waters of fountains or springs, are mel- ted snow, rain water, and condensed va*- pours.
Springs, Rivers, and the Sea* i2£
The prodigious quantity of vapours raised by the sun's heat, and otherwise, being carried by the winds over the low lands to the very ridges of mountains, as the Pyrenean, the Alps, the Apennine, the Carpathian, in Europe ; the Taurus the Caucasus, Imaus and others in Asia ; Atlas the Monies Lunce, or mountains of the moon, with other unknown ridges in Africa ; the vapours being compelled by the stream of air to mount up with it to the top of those mountains, where the air becoming too light to sustain them, and condensed by cold they strike against their summits^ which causes an union of their particles, and are precipitated in water, which gleets down by the crannies of the stone ; and entering into the ca- verns of the hills, gathers, as in an alem~ lie, into the basons of stone it finds, which being once filled, all the overplus of water that comes thither, runs over by the lowest places, and breaking out by the sides of the hills forms single spmgs.
Many of these springs running down
by the vallies, between the ridges of the
hills, and coming to unite, form little
rivulets, or brooks ; many of these agaia
JL
1 26 Springs, Rivers, and the Sea.
meeting in one common valley, and gam- ing the plain ground, being grown less rapid, become a river; and many of these being united in one common chan- nel, make such enormous streams as the Rhine, the Rhone and the Danube. And it may almost pass for a rule, that the magnitude of a river, or the quantity of water it discharges, is proportional to the length and heights of these very ridges from whence the fountains arise.
The several sorts of springs observed are common springs, which either run continually, and then they are called perennial springs ; or else run only for a time, or at certain times of the year, and then they are called temporary springs. Intermitting springs, or such as flow and then stop, and flow and stop again, by regular alternations or intermissions, Reciprocating springs, whose wraters rise and fall, or flow and ebb, by regular in- tervals, or reciprocations of the surface.
If those reservoirs of water in the bo- dy of mountains be situated where min- eral ores abound, or the ducts or feeding streams run through mineral earth, it is easy to conceive the particles of metal
Springs, Rivers-^ and the Sea. 127
will mix with, and be absorbed by the water, which being saturated therewith, becomes a mineral spring or well. If salt, sulphur, and lime-stone abound in the strata through which the water pas- ses, it will then be saline, sulphureous, and lime-water. If sulphur and iron should both 4 abound in the parts of the hill, whence the waters come, the waters will partake of the warmth or heat, which is. occasioned by the mixture of two such substances in the earth, where they are found.
Having noticed the different kinds of springs, we shall say a few words respec- ting the various phenomena which take place in rivers.
A large collection of water which runs in consequence of its gravity from at higher to a lower pare of the surface of the earth, in a channel generally open at top, is called a river.
A river which flows uniformly, and preserves the same height in the sa-ne place, is said to be in a permanent state ; such rivers are very rare.
The water of a river does not flow with the same velocity through the
128 Springs, Rivers, and the Sea.
whole width of the river. The line in which the water moves with the greatest velocity is called the thread of the river, and this thread seldom lies in the middle of the river, but it generally comes near- er to one side than the other, according to the nature of the impediments, and the configuration of the banks. The ve- locity of rivers is likewise less at the bottom of their channels, than at their surface ; owing to the resistance which the bed makes to the water as it flows.
The running of rivers is upon the same principle as the descent of bodies on in- clined planes ; for water no more than a solid can move on a horizontal plane, the re-action of such a plane being equal and contrary to gravity entirely destroys it, and leaves the body at rest; here we speak of a plane of small extent, and such as co- incides with the curved surface of the earth. But if we consider a large extent or long course of water, then we shall find that such water can never be at rest but when the bottom of the channel coincides every where with the curved surface of the earth. In rivers that are made it is usual to allow the fall of 1 foot in 300, but
Springs, Rivers, and the Sea. 129
the declivity of those formed by nature is \rarious and uncertain.
The velocity of the water of a river Ottght to increase in proportion as it re- cedes from its source : but the numerous causes of retardation, which occur in riv- ers, are productive of very great irregu- larities ; and it is impossible to form any general rules for determining such irregularities.
The unequal quantities of water (ari- sing from rains, from the melting of snow &c.) which are conveyed by rivers at dif- ferent seasons, enlarge or contract their widths, render them more or less rapid, and change more or less the form of their beds. But independent of this, the size and form of a river is liable to be continu- ally altered by the usual flowing of its waters, and by local peculiarities. The water constantly corrodes its bed where- ver it runs with considerable velocity, and rubs off the sand, or other not very coherent parts. The corrosion is most remarkable in that part of the bottom, which is under the thread 'of the river, or where the water descends suddenly from an eminence, as in a cascade or water -fall* L2
1 3O Springs , Rivers, and the Sea.
The sand thus raised is deposited in pla- ces where the water slacks its velocity, and there by degrees an obstacle, a bank, and even an island, is formed, which in its turn produces other changes. Thus a river sometimes forms itself a new bed, or it oversows the adjacent grounds. k
In some places we find that an obstacle or a bent on one side will occasion a cor- rosion on the opposite bank, by directing the impetus of the stream towards that bank. — Thus, from divers causes, whose concurrence in different proportions, and at different times, forms an infinite varie- ty, the velocity of rivers is never steady or uniform.
The following curious calculation res- pecting the river Thames was made by Dr Halley. " In order to estimate the quanti- ty of water, which passes daily through the Thames, the Doctor assumes the breadth of the river at Kingston bridge, (where the flood seldom reaches) to be 100 yards, and the depth 3 ; so that the section of the channel is 300 square yards, and allowing the velocity of the \vater to be at the rate of 2 miles per hour, there will run in 24 hours, the length of 48 miles
Springs, Rivers, and the Sea. 131
or 84480 yards ; therefore 84480 x SOOzz 25,344,000 cubic yards, which make 203,- 000,000 tons which the river Thames yields per diem.
The proportional lengths of course of some of the most noted rivers in the world are shewn nearly by the following num- bers, extracted from Mr. RennelPs paper 71st vol. Phil. Trans.
European Rivers.
Thames 1
Rhine 5~
Danube 7
Wolga 9|
Asiatic Rivers.
Indus 5^
Euphrates . . 8-|
Ganges 9-|
Burrampooter 9-|
Nou Kian, or Ava River . . 9-|
Jennisea 1O
1 Oby 10!
Amoor 11
Lena 11-J
Hoanho (of China) .... 13A Kian Keu (of ditto) . . , 15|
132 Springs, Rivers, and the Sea. African River.
Nile
American Rivers. Mississippi ........ 8
Amazons ......... 15|
When we reflect on the immense length of these rivers, and their origin, we are naturally directed to the contemplation of the round which water travels ; and by which, without suffering adulteration or waste, it is continually offering itself to the wants of the habitable globe. From the sea are exhaled those vapours which form the clouds ; these clouds descend in refreshing showers of rain, which sinking deep into the earth, form springs, and springs uniting form rivers, which rivers in return feed the ocean. So there is an incessant circulation of the same fluid; and not one drop probably more or less now than there was at the creation. In fact, " look nature through, 'tis revolution all'* wherever we turn our eyes, all seems continually in a state of change or circu- lation. a The sun," saith Solomon, " ari- seth, and the sun goeth down, and pants
Springs, River s^ and the Sea.
for the place from whence he arose ; all rivers run into the sea, yet the sea is not full ; unto the place from whence the ri- vers came, thither they return again."
The Sea is a vast collection of waters in the deep and unfathomable valleys of the earth. This great abyss occupies nearly three quarters of the whole surface of our globe ; which has been thought by some too great a proportion ; but it is probably no more than sufficient to fertilize the land.
The saltness of the sea is a property in that element, which appears to have exci- ted the curiosity of naturalists in all ages. This property is very rationally judged to arise from great multitudes both of mines and mountains of salt, dispersed here and there in the depths of the sea ; the salt being continually diluted and dis- solved by the waters, the sea becomes im- pregnated with its particles throughout ; and for this reason the saltness of the sea can never be diminished.
The saltness of the sea preserves its waters pure and sweet, which otherwise would corrupt and stink like a filthy lake, and consequently none of the myriads of
1 34 Springs, River s^ and the Sea.
creatures which now live therein, could then have being ; from hence also the sea water becomes much heavier ; and there- fore ships of greater size and quantity may be used thereon. Salt water also doth not freeze so soon as fresh water, whence the seas are more free for navi- gation.
The most re mark able thing in the sea, is that motion of the water called tides. It is a rising and falling of the water of the sea. The cause of this is the attraction of the moon, whereby the part of the water in the great ocean which is nearest the moon being most strongly attracted, is raised higher than the rest ; and the part opposite to it, on the contrary side, being least attracted, is also higher than the rest. And these two opposite rises of the sur- face of the water in the great ocean, fol- lowing the motion of the moon from east to west, and striking against the large coasts of the continents that lie in their way, from thence rebound back again, and so make floods and ebbs in narrow seas, and rivers remote from the great ocean.
As the earth, by its daily rotation round its axis, goes from the moon to the moon
Springs, Rivers, and the Sea. 135
again (or the moon appears to move round the earth from a given meridian to the same again) in about 24 hours, hence in that period there are two tides of flood and two of ebb, and this alternate ebbing and flowing continues without intermis- sion. For instance, if the tide be now at high -water-mark, in any port, or harbour, ivhich lies open to the ocean, it will pres- ently subside, and flow regularly back, for about six hours, when it will be found at low-water-mark. After this, it will again gradually advance for six hours, and then return back, in the same time, to its for- mer situation; rising and falling alternate- ly, twice a day, or in the space of about twenty- four hours.
The interval between its flux and reflux is, however, not precisely six hours, but about eleven minutes more ; so that the time of high water does not always happen at the same hour, but is about three quar- ters of an hour later every day, for thirty days ; when it again recurs as before. For example, if it be high water, at any place, to day at noon, it will be low water at ele- ven minutes after six in the evening ; and consequently, after two changes more, the
136 Springs, Rivers, and the Sea.
time of high water the next day will be about three quarters of an hour after noon; the day following it will be at about half an hour after one ; the day after that at a quarter past two; and so on for thirty days when it will again be found to be high wa- ter at noon, the same as on the day the observation was first made. And this ex- actly answers to the motion of the moon ; she rises every day about three quarters of an hour later than upon the preceding one; and, by moving in this manner round the earth, completes her revolution in a- bout thirty days, and then begins to rise again at the same time as before.
To make the matter still plainer ; sup- pose, at a certain place, it is high water at three o'clock in the afternoon, upon the day of the new moon ; the following day it will be high water at about three quar- ters of an hour after three ; the day after that at about half an hour past four ; and so on, till the next new moon ; when it will again be high water about three o'- clock, the same as before. And by obser- ving the tides continually at the same place, they will always be found to follow the same rule ; the time of high water,
Spri ngs, Rivers, and the Sea. 137
Upon the day of every new moon, being nearly at the same hour ; and three quar- ters of an hour later every succeeding day*
The attraction of the sun also produ- ces a similar rising and falling of the wa- ter of the ocean, but on account of its dis- tance, not near so considerable as that which is produced by the moon* It will be readily understood that according to the different situations of the sun and the moon, the tides which are raised by their respective attraction, will either con- spire with, or counteract each other in a greater or lesser degree. When they con- spire together the tides rise higher, and their mutual action produces what are cal- led spring1 tides* On the contrary, when they counteract each other they produce ntap tides. \
From a slight consideration of what has been said, we might be led to imagine that the time of high water at any place, would be when the moon is over the me* ridian of that place. But this is by no means the case ; it being usually about three hours afterwards : the reason of which may be shown as follows. The moon3 when she 15 on the meridian, or M
Springs^ Rivers*) and the Sect.
nearest to the zenith of any place, tends to raise the waters at that place ; but this force must evidently be exerted for a con- siderable time, before the greatest eleva- tion will take place ; for if the moon's at- traction were to cease altogether, when she has passed the meridian, yet the mo- tion already communicated to the waters would make them continue to ascend for some time afterwards,* and therefore, they must be much more disposed to ascend when the attractive force is only in a small measure diminished.
The waves of the sea, which continue after a storm has ceased, and almost eve- ry other motion of a fluid, will illustrate this idea ; all such effects being easily ex- plained, from the consideration that a small impulse, given to a body in motion,, •will make it move farther than it would otherwise have done. It is also, upon the same principle, that the heat is not the greatest upon the longest day, but some time afterwards ; and that it is not so hot at twelve o'clock, as at two or three in the afternoon ; because there is a farther in- crease made to the heat already imparted. Instead of its being high water then, when
Springs, Rivers^ and the Sea. 139
the moon is upon the meridian of any place, it will always be found to happen, as far as circumstances will allow, about three hours afterwards ; and the intervals between the flux and reflux, must be reck- oned from that time in the same manner as before.
The sun being nearer the earth in win- ter than in summer, is nearer to it in Feb- ruary and October than in March and September ; and therefore the greatest tides happen not till some time after the autumnal equinox, and return a little be- fore the vernal.
The tide propagated by the moon in the German ocean, when she is three hours past the meridian, takes twelve hours to come from thence to London Bridge ; where it arrives by the time that a new tide is raised in the ocean.
These are the principal phenomena of the tides ; and where no local circumstan- ces interfere, the theory and facts will he found to agree. <But it must be observed that what has been here said, relates only to such places as lie open to large oceans. In seas and channels, which are more con- fined, a number of causes concur, which
140 Springs j Rivers, and the Sea.
occasion considerable deviations fiom the general rule. Thus, it is high water at Plymouth about the sixth hour ; at the Isle of Wight about the ninth hour ; and at London bridge about the fifteenth hour after the moon has passed the meridian. And at Batsha, in the kingdom of Ton- quin,the sea ebbs and flows but once a day the time of high water being at the setting of the moon, and the time of low water at her rising. There are also, great varia- tions in the height of the tides, according to the situation of coasts, or the nature of the. straits which they have to pass through. Thus, the Mediterranean and Baltic seas have very small elevations ; while, at the port of Bristol, the height is sometimes near thirty feet ; and at St. Malo's it is $aid to be still greater.
Fvssik* 1.41
CHAP. IX.
Of Earths, Stones, Metals, Miner- als, and other Fossils.
HAVING taken a view of the air which surrounds, and the water which diversifies the face of our globe, we will now take a survey of the solid substance, or body of our earth.
Those who observe the disposition of the earth, as it appears in the quarrying or digging of mines, find it generally ly- ing in horizontal layers, or strata of dif- ferent kinds, like the settlings of waters* The first layer that presents itself, is most commonly the bed of vegetable earth or mould. With this earth the surface of our globe is generally covered* It is this mould which gives rooting and nour- ishment to plants, so that they may stand and grow in it, and it is as it were the store-house from whence all the living M2
142 Fossils.
creatures of our world have originally their provisions ; for from thence all the plants have their sustenance, and some few animals, and from these all other an- imals.
As this affords to animals and vegeta- bles their support, so the spoils of these, when dead or decayed, return to the dust of the ground, from whence they were formed, and thus keep up an unceasing circulation.
The most common disposition of the layers is, that under the first earth is found gravel or sand ; clay or marl ; then chalk, or coal, marbles, ores, &c. This disposition, however, is far from being uniformly continued all over the globe ; in different soils the order of these layers vary.
It is wonderful the variety of produc- tions which are found in the different parts of our globe. In the crumbling chalk, the solid marble, the dusty gravel, and even the depths of the most inland valleys, and on the summits of the high- est mountains, we behold the spoils of the ocean, exhibited under the several ap- pearances of petrified fish, beds of shells^
Fossils. 143
and sea plants. The Alps, the Apen- nines, the Pyrenees, Libanus, Atlas, and Ararat, every mountain of every coun- try under heaven, where search has been made, all conspire in one uniform and universal proof, that the sea has covered their highest summits. If we examine the earth, we shall find the mouse deer, natives of America, buried in Ireland ; elephants, natives of Asia and Africa, buried in the midst of England ; croco- diles, natives of the Nile, in the heart of Germany ; shell-fish, never known but in the American seas, together with skel- etons of whales, in the most inland re- gions of England ; trees of vast dimen- sions with their roots and tops at the bot- tom of mines and marls, found in regions where such trees were never known to grow, nay, where it is demonstrably im- possible they could grow. Such are the awful memorials of the great convulsions and revolutions which have taken place in the natural world ; of countries laid under the rolling waves of the ocean ; and of lands rising from the midst of the waters, and becoming the habitations of beasts and of men ; so transient fiiicl un certain are all earthly things.
144 Fossils.
The various bodies which are found by digging in the earth are called fossil substances \ under which are comprehen- ded metals, minerals, stones of divers kinds, and sundry bodies that have the texture between earth and stone.
These bodies are divided into four different classes by mineralogists, viz. I. Earth and Stones in general ; II. Salts ; III. Inflammables ; and IV. Metals.
I. Earth and Stones in general are 1st, mould the support of vegetables; 2nd, clays, which mixed with water harden in the fire, into bricks, delf, china, &c. 3d, calcareous substances, as chalks, marls, limestones, marbles, convertible by heat into quicklime, and gypsum into alabas- ter ; 4th, talcs, which are found in flat, smooth laminae ; 5th, slates also split into laminae ; these with a variety of stones from freestone, or sand, to granite, por- phyry, flint, and substances still harder, such as precious stones, are known by va- rious properties, and are accordingly ap- plied to different purposes ; some, in ad- dition to being serviceable in building, are used as whetstones ; some strike fire with steel ; others are polished to glitter in the
Fossils.
dress ofthe fair, or decorate the furniture of the opulent ; and others, melted by fire, form the transparent glass.
Although there seems to be an almost infinite variety of earthly substances scat- tered on the surface of this globe yet when we examine them chemically, \ve find that all the earth and stones which we tread under our feet, and which compose the largest rocks as well as the numerous different specimens which adorn the cabi- nets of the curious, are composed of a very few simple or elementary earths, the principal of which are the calcareous, si- liceous, argillaceous, magnesia, terra pon- derosa, and a few others which have been discovered lately, but have not been much examined.
Calcareous earth is found in the shells of fishes, the bones of animals, chalk, limestone, marble, and gypsum : but all calcareous earth is supposed to be of animal origin ; and beds of chalk, lime- stone, or marble, are thought to have been beds of shells formed in the sea, in some pristine state of the earth.
Silex, or siliceous earth is the princi- pal constituent part of a great number of
146 Fossils.
the compound earths and stones, forming the immense mass of the solid nucleus of the globe. It is the base of almost all the scintillating stones, such as flint, rock, crystal, quartz, agate, calcedon, jasper, &JV. The sand of rivers and of the sea-shore, chiefly consists of it.
Argillaceous earth is found in clay^ schistus, or slate, and in mica. This species of earth is ductile with water, it then hardens and contracts by heat, so as to be of the greatest use in forming brick, or stones of any required form or size.
Terra ponder osa is generally found in two states, viz. united to vitriolic acid, when it is called calk; or to fixed air, when it is called terra ponderosa aerata. This earth is distinguishable by its great speci- fic gravity, being four times as heavy as water.
Magnesia is found sometimes pure in nature, but it is generally obtained by art from some of its combinations. It gives a peculiar character to the substances of which it forms a part. The stones which contain magnesia in considerable quantity ' .have generally a smooth and unctuous feel?
Fossils. 147
a greenish cast, a fibrous striated tex- ture, and a silky lustre. Among them we may mention talc, steatite, serpentine, chlorite, asbestos, &c. Pure magnesia does not form with water an adhesive duc- tile mass. It is in the form of a very white spongy powder and perfectly tasteless.
Stones are formed by the mixtures of the earths together, and of the mixtures of earths with alkalies, and sometimes with acids. Stones bound together by some cement, form rocks. There is also a kind of stones of a peculiar nature produced by the fire of volcanoes.
The stones in which the acids and al- kalies abound are called saline stones, and the mixtures of the earths with each oth- er form stones properly so called. Of stones properly so called, those in which the siliceous earth abounds and predom- inates are very numerous ; the principal of which we shall briefly notice.
Siliceous mixtures have sufficient hard- ness to strike fire with steel. Of this de- scription are the precious stones, rock crys- tat, or quartz, felspar, silex, crysopryse^ lapis lazuli, jasper, and schorl*
148 fossils.
Gems, or precious stones, are of various kinds. They are distinguished by their hardness, weight, colour, and splendour^ as well as by their property of producing single or double refractions. As their colour is, of all their characters, the most apparent, it is according to this that we shall divide them.
Red gems are the ruby, the vermillion9 garnet and girasol. The ruby is a trans- parent stone, the colour of which is more or less red. It is distinguished into four kinds, viz. the oriental ruby, the spinel ruby, the balass ruby, and the Brazilian ruby.
fellow gems are the topaz, hyacinth and jargon of Ceylon. Of the topaz, there are three kinds, the oriental topaz, the Bra^ zilian topaz, and the Saxon topaz.
Blue gems are the sapphire,a.ud the aiguc marine. There are two kinds of the sap- phire, viz. the oriental sapphire, and the Brazilian. There are also two kinds of the aigue marine, the oriental and the occidental.
Green gems are the emerald of Peru and the chrysolite, of which there are two kinds, viz. the Brazilian, accl that of the jewellers.
fiossik. 149
The diamond ought certainly to be pla- ced among the precious stones, but it is different from all those above described. Its combustibility is a property entirely peculiar to itself; the diamond indeed burns hi the same manner as phosphorus, disappears without leaving any vestiges of it behind. The diamond is supposed to be pure carbon, and the radical of the carbonic acid.
There are several varieties of the dia- mond, which differ from each other only in colour ; some are^f a rose colour, and others red, orange, yellow, green, blue and dark coloured.
Rock-crystal and quartz seem to be the same stone* The name of rock-crystal is given to that which is crystallized, and of quartz to that which is in a rude mass. The form of these crystals is a hexadral prism, terminated at one of its extremities and sometimes at both, by a summit com- posed of six triangular faces. In hardness they are inferior to all the other gems. Rock-crystal consists almost entirely of pure silex. Quartz enters into the com- position of granite.
Freestone is of the same i^ature as N
130 Fossils.
quartz. It is granulated, being composed of sir. all grains of quartz, cemented toge- ther, but which have very little adhesion.
Fehpar is inferior in hardness to quartz. It fuses by the action of heat, and forms white enamel. It is one of the constituent parts of porcelain.
We may mention, under this class, ad- amantine spar, which approaches near to the preceding in its appearance and frac- ture, but which differs from them con- siderably, by its great hardness, its form, and gravity. It is so exceedingly hard, thai it may be employed to cut the dia- mond.
Flint is a stone * which is so hard as to strike fire with steel, Among the dif- ferent \ rid of flints, some change their colour according to the directions of the rays of light, and others do not. Of the former there are three, the opal, the cat's- eye and iheji.s/i-et/e.
The kinds of flints which do not change their colour according to the direction of the rays of light, exhibit tints of more or less brightness, and are susceptible of a fine polish. We are acquainted with eight kinds of them, viz. common Jtint^
Fossils. 1 5 ':
petro si lex, agate, calcedony, cornelian, 3arcknyx,\\\zjade, and iheprasium.
Common flint posesses very little transparency. All the different kinds of it have a dark dull colour, and are con- cave, or convex, on the fracture. They do not fuse in the fire, but are calcined and become white.
The distinguishing character of petro silex is its semi-transparency, similar to that of wax. It becomes white in the fire, like the common flint, but it is more fusible, as it runs without any addition.
Agate has a smooth shining fracture, and will take a very high polish ; it is much variegated. When exposed to heat, it loses its colour, and becomes o~ paque, but without fusing.
The calcedony has a milky semi-trans- parency. Every kind of it takes a fine polish. These stones are white, inter- mixed sometimes with tints of red, yel- low, and blue.
The cornelians are all either entirely^ or in part, of a beautiful red colour, but they lose their colour in the fire, and be- come opaque. They are all susceptible of a fine polish.
152 Fossils.
Lapis lazuli is of a beautiful sky- blue colour, sometimes mixed with white, and is entirely opaque. It is sometimes mixed with pyrites, from which it has been supposed that it contained gold. If exposed to a strong heat, it fuses, and forms a sort of whitish glass ; when cal- cined, it dissolves in acids into a kind of jelly. Lapis lazuli, when pulverized, forms that valuable colour known under the name of ultramarine.
Jasper is a stone which exhibits every variety of colour. It is exceedingly hard, and receives a very beautiful and dura- ble polish. When exposed to the action of heat, it does not fuse.
Schorl is a hard stone, fusible in a moderate fire, without any addition. Its crystals exhibit a great variety, in regard to form, appearance, texture, structure, &c. Schorl, in general, is opaque ; some kinds, however, are transparent, such as Brazilian emerald, the peridot^ the tour- malm, &?c.
The colour of schorl is various ; some, kinds are black, others violet, and some green. Schorl enters into the composi- tion of porphyry, serpentine, the ophite, granitelL and granite.
Fossils. 153
The primitive earths form stones, as we have mentioned, and stones united by cement form those masses called rocks. We shall notice the six mixtures which are most commonly found in those mas- ses, viz. porphyry, serpentine, ophites granitell, granite, andjtint.
Porphyry is composed of felspar in small fragments, of schorl, and a kind ot cement, which unites ail the parts, and which, in some measure, forms the base. Porphyry is exceedingly hard, and diffi- cult to be cut j it will, however, take a fine polish. Some kinds of it are red, and others green.
Serpentine is composed of the same substance as porphyry. The only differ- ence is, that the felspar is in larger frag- ments. The colour of serpentine is vari- ous ; some kinds are green, others violet, some yellow, and some black.
The ophite is composed of only two substances, viz. black schorl, known un- der the name of ancient black basaltes, interspersed with greenish felspar, which forms in it long spots. This stone has considerable hardness. N2
154 Fossils.
Granitell is also composed of two sub- stances ; black schorl, and white felsper, mixed with some of the green felspar. — The only difference then between the granitelles and the ophite is, that the schorl which enters into the composition of the former is not of the same kind as that in the latter.
Granite is composed of felspar, schorl, and quartz. The colour of granite is various ; it is hard, difficult to be work- ed, and receives a fine polish-
Flint is a hard opaque stone, suscepti- ble of a very beautiful polish. It appears to be composed of concentric strata, and has considerable brilliancy on its frac- ture. Flints are never found in continued quarries, like the other stones ; they are found detached, and dispersed through- out the fields. When joined by any kind of cement they form pudding-stones. They become decomposed in the air, for they are found for the most part covered •with a crust, of a softer nature than the interior part. Their colour is exceeding- ly various ; some of them are spotted and yariegated with veins, others exhibits the resemblance of plumes, and even of plants.
155
Vakonic Productions are chiefly pum- ice-stones, lava and basaltes.
Pumice-stone is real glass, in the form of small greyish, white, and exceeding- ly brilliant filaments. These filaments always leave vacuities of greater or less size between them, which occasions great variations in its specific gravity. In general it is lighter than water.
Lava is that burning matter which runs down, in such prodigious quantities, from volcanoes, when in a state of eruption., and often extends to a great distance. This matter is a semi-vitrified substance, which appears blackish, on account of its density.
Basaltes is blackish and opaque. By the action of heat it may be converted into glass, of a very beautiful black co- lour. It often crystallizes in prisms, of three, four, five, six, or seven planes- Of some kinds, such as that known un- der the name of touchstone, the grain is exceedingly fine.
II. Of Salts. — The alkalies, the acids, and the combinations in which they enter insufficient quantities, are called salts ,
156 Fossils.
or saline substances; for a saline sub- stance, in its extended chemical sense, means a substance that has some taste, and is soluble in water. These sub- stances, however, do not strictly and ex- clusively belong to the fossil department, but are obtained also from animal and vegetable substances. They are the most active agents in creation. They give bodies their consistency ; preserve them from corruption, and render them sa- voury.
Alkalies are distinguishable by their acrid, burning, and urinous taste, their causticity, their singular action on the skin and all animal substances, the quali- ty of changing the blue colour of violets to a green, and even a greenish yellow, and deliquescency. We are acquainted with three species, — potash, soda, and ammonia. The first and second have been called fixed alkalies, because they melt and grow red in the fire before they become volatile ; the third has been named volatile alkali, from possessing the opposite property.
Potash is known by the following char- acters :—It is dry, solid, white, and very
Fossils. 157
deliquescent, absorbs water with heat and a peculiar faint smell, combines with siliceous earth by fusion, and forms glass. It is frequently found native with lime, and combined with different acids ; but is chiefly obtained from vegetables, in the ashes of which it remains after com- bustion.
Soda or the mineral alkali, is procured from the ashes of sea-weed, and consti- tutes the basis of sea-salt. It strikingly resembles potash in form, causticity, fusi- bility, deliquescency, combination with earthy substances, by means of fusion, action on animal substances, Sec. so that it was long confounded with it, and might have continued to be so, if it did not form very different salts with acids, and yields these acids to potash.
Ammonia, or volatile alkali, differs greatly from the two preceding species in its form of gas when dissolved in cal- coric, in its liquid form when dissolved in water, in its pungent and suffocating smell, its solubility in air, &c. Am- monia is procured by burning animal substances ; in Egypt, (from whence, as contained in sal ammoniac we till of late
158 Fossils.
imported it) from camels' dung ; but now from bones by distillation.
All Acids appear to be combinations of oxygen or vital air, with elementary sub- stances. Their taste is sour, as their name imports. They change most of the blue vegetable colours red, and have a tendency to combine with earths, alka- lies, and metallic substances.
All acids, being compounds of oxygen with different substances, the former prin- ciple is the cause of their resemblance and common properties ; the latter, being different in each, may serve to character- ize each in particular. For this reason those matters which are variable in acids are termed their radicals, or acidifiable principles. Thus all acids are combina- tions of radicals, or acidifiable substan- ces, different in each species, with oxy- gen, which is the same in all : whence it follows, that their common properties, their characters as acids, depend on oxy- gen, which is the acidifying principle ; their particular properties, their specific characters arise from their radicals. The word acid, indicating the general and identical nature of these substances, forms their generical name, while the particular
Fdssifo* 159
name of the radical contained in each may with propriety designate each particular acid. — Thus sulphur is the radical of the acid we name sulphuric, phosphorus that of the phosphoric, carbon that of the carbonic, and so on.
Acidifrable radicals may contain differ- ent quantities of oxygen, .and under this point of view they possess two states of acidity. The first is that, in which they contain the least possible quantity of oxy- gen to render them acid. In this their acidity is commonly weak, and they adhere but feebly to the bases with which they are capable of forming salts. The mod- ern methodical nomenclature designates this state of combination and acidity ^ by giving the names of these weak acids the termination ous. Thus wre say the sulphu- rous, nitrous, phosphorous, or acetous^ acid. The second state of acids is that,, in which they contain more oxygen, and in general are completely saturated with it. In this they have all the strength and attraction they are capable of possessing as acids, and the modern nomenclature expresses it by the termination zc. Thus we say the sulphuric, nitric, phosphoric,,
16O Fossils.
or acetic, acid. With regard to the pro* portion of oxygen united to acidifiable ra- dicals, still greater latitude may be given to the considerations presented above. Each radical may be contemplated in four states : 1st, containing very little oxygen not sufficient to impart to it the nature of an acid, and in this it is nothing more than an oxyd ; such is sulphur coloured red or brown, by exposure to the air, and a de- gree of heat inadequate to produce infla- mation ; when it is oxyd of sulphur ; 2dly containing more oxygen than in the pre- ceding case, and enough to become an a- cid, though weak ; as in the sulphurous acid ; 3dly, possessing still more oxygen than in the second instance, and having acquired powerful acid properties ; such as the sulphuric acid ; ithly, conjoined with a larger dose of oxygen than is neces- sary to constitute a powerful acid, an acid in ic ; when it is termed an oxygenated acid, or even super-oxygenated.
The acids are generally divided into mineral, vegetable, and animal, acids, ac- cording to the nature of their radicals. Though the first class only with propriety claims notice in this place, yet for the in-
Fossils. 161
formation of the reader we will enumerate those belonging to each of the above classes.
The miner a I acids at present known are the sulphuric (formerly called the vitriolic acid); the nitric acid, called also aquafor- tis; the muriatic or marine acid, called by artizans the spirit of salt ; the carbonic acid, formerly called the acid of charcoal, aerial acid, or fixed air, &c. the phospho- ric acid, which is likewise an animal acid, it being found amongst animal matters as well as among minerals ; the acid of bo- rax ; the flouric acid, formerly called the acid of spar /the arsenic acid ; the moiyb- die acid ; the tungstenic acid ; and the chromic acid. The last four are also called metallic acids.
The vegetable acids are the acetic, or vinegar, the acid of tartar, the empyreu- matic acid of tartar, the oxalic or acid of sorrel, the acid of galls, the citric or lem- on acid, the malic or acid of apples, the benzoic, or the acid of benjamin, the em- pyreumatic acid of sugar, the acid of cam- phor, and the suberic or acid of cork.
The animal acids are, the acid of milk, the acid of sugar of mu% the formic or a- O
162 Fossils*
cid of ants,the prussic acid, viz. the colou- ring matter of prussian blue, which is ob- tained from dried blood, hoofs, &c.the se~ bacic or acid of fat, the bombic or acid of silk- worms, the laccic or the acid of waxy matter, and the zoonic, or the acid extrac- ted from animal matter by means of lime.
For a more full account of these acids we refer the reader to various recent pub- lications, written professedly on the sub- ject of chemistry.
Acids and alkalies, shew strong attrac- tions for each other, and when combined together in such proportion that neither of them predominates, form neutral salts : substances altogether dissimilar to the elements of which they are composed. The salt in common use for instance, is formed of mineral acid and alkali ; either of which, singly, would be hurtful to the human body ; and the acid, in particular, would be extremely pernicious.
Each acid produces with each of the three alkalies a particular neutral salt. The number of the last may therefore be found by multiplying the number of the acids which we know, by three^ the number of the alkalies*
Fossils*
III. Inflammables. — Inflammables are sulphur or bitumens. These substances are both derived from the spoils of vege- tables and animals.
Sulphur, known also by the name of brimstone, is a simple combustible sub- stance, which nature frequently presents in a pure state. It is found in the earth in a loose powder, or solid ; and either detached or in Veins. It is met with in the greatest plenty in the neighbourhood of volcanoes, and is deposited as a crust on stones contiguous to them. It is al- so met with in mineral waters, coal-mines, £?c. and also in combinations with most of the metals.
The bitumens are naptha, petrol, min- eral tar, asphaltum,jet, cannel-coal, min- eral tallow, pit-coal, amber, &c.
Naptha is a white or yellowish white substance, fluid as water, feels greasy, has a penetrating smell, and burns with a light flame,leavmg scarcely any residuum.
Petrol, or Petroleum, is a brown semi- transparent substance ; being naptha, thickened, and altered in colour and other respects by the air.
164 Fossils.
Mineral Tar is petrol farther altered by the air, having become of the colour and consistency of pitch.
Asphaltum, or mineral pitch ^ is produ- ced by a still farther exsiccation or drying.
Jet is a substance of a full black, hard- er, and less brittle than asphalt ; and ac- cording to Wtdcnrnan, is a species of coal.
Cannell'Coal appears to be next to jet, in gradation, of the compound mineral bituminous substances.
Mineral Tallow is rarely met with, and imperfectly known. It much resembles tallow.
Mineral Caoutchouc is a substance much resembling, in its elastic properties, the substance from which it takes its name.
Pit-coal, according to Mons. Gensannc and others, is an earth or stone, chiefly of the argillaceous genus, penetrated or im- pregnated with petrol or asphalt. It has also been supposed to hav7e been formed by vegetables growing in the sea, and by vast forests which have been buried br subsequent revolutions,
Fossils* 1 6-5
Amber is a bitumen generally of a yel- low or brown colour. It is found either under the surface of the ground, among the clay, sand, and iron bog ore, when it is called yissz/ amber, or is thrown on the shore by the waters of the sea, and is then called mineral amber. It is tasteless, but when rubbed it yields a faint odour, and manifests electric powers.
IV. Metals. — We are at present ac- quainted with twenty -one metallic sub- stances, essentially different from each other; gold,platina, silver, mercury, lead, copper, iron, tin, zinc, bismuth, antimony, arsenic, cobalt, nickel, manganese, molyb- dena, wolfram, chrome,uranium,titanium% and tellurium.
Metals exceed all other fossils in spe- cific gravity ;* but there exists, in this
*The specific gravity of any body is the proportion which its weight bears to the weight of another body of equal bulk. The established custom is to compare all bodies with water, the specific gravity of which is reckoned one, or unity; so that when the specific gravity of anybody, asGold,for instance, 5s said to be 19, Zinc 7, we mean that equal quan- tities of Water, Gold, and Zinc weigh respectively 1, 19, and 7, be they pounds, ounces, grains, or any other weights. O2
166 Fossils.
respect, a remarkable difference among themselves. They are completely opaque. They also possess a mirror-like lustre, which is one of their characteristic marks and they present a convex surface when melted in earthen vessels. Besides, they are all insoluble in water. And by these external characters, it is easy to distin- guish this class from all other fossils, viz. earths, salts, bitumens, and sulphur.
Metals are concealed in the earth, and form ores, which existing in crevices of rocks, are called ^Z72,9,and are distinguish- ed into level, or into inclined, direct or oblique, according to the angle they make with the horizon. The part of the rock resting on the vein, is termed, the roof; and that on which the vein rests, the bed of the vein. And the cavites made in the earth, in order to extract these ores, are called mines.
When nature has bestowed on metals their proper metallic appearance, or they are only alloyed with other metals, they are said to be native. When combined, as they commonly are in mines, with some unmetallic substance, thev are said to be mineralized ; the substance that sets them
Fossils. 16f
in, that state, is called a mineratizer, and the compound of both, an ore ; which term is applicable when stones, or earths, con- tain metallic substances, \vhether native or mineralized, in a notable proportion.
Several metals are ductile and mallea- ble, and their parts may be displaced from each other by compression, or hammer- ing, without losing their cohesion. Hence., some of them may be stretched out to thin laminae, or drawn into slender fila- ments ; as, for instance, gold, silver, plan- tina, copper, lead, tin, and iron. — Other metals are fragile, or brittle, and do not admit of being stretched and extended ; such are antimony, arsenic, cobalt, bis- muth, &Pc.
All metals are fusible, but not all in the same degree ; thus mercury is mel- ued even by the usual temperature of our atmosphere. — Some metals, as tin and ^ead, melt even before ignition ; others, as silver, gold copper, iron, fuse only af- ter being ignited.
All metals, iron and platina only excep- ted, melt on a sudden, as soon as they are heated in a due degree ; but iron and platina grow soft before they fuse..
168 Fossils.
and on this depends their very useful property of becoming capable of being -welded.
Almost all metals may be combined by fusion into one seemingly homogene- ous mass, and from thence various metal- lic mixtures, metallic alloys, or composi- tions arise ; which, for their particular properties, are often of very great utility.
If metals be continued in fusion, the} lose their brilliancy, and become an opaque powder, or what is termed a metallic oxyd or calx.
All metals, gold, silver, and platina, excepted, are oxyded or calcined in fire with access of air. In this respect, those •which cannot be oxyed by fire have recei- . ved the name of noble metals, to distin- guish them from the rest which may be calcined that way, and are called base metals.
Gold is a noble metal, of a yellow colour; and, after platina, the heaviest of metals. Its specific gravity is from 19,258 to 19,- 640. Its hardness and elasticity are in- considerable ; but its tenacity is great ; and with regard to ductility, or malleabili- ty it exceeds all other metallic substances.
Fossils. 169
Platma is a noble metal of a white co- lour ; for which reason some called it •white gold. In Europe it is known only since the middle of the present century, and brought to us in small irregularly-fig- ured grains, but which are impure, and mostly contaminated with iron. Pure platina exceeds all other metals, even gold In specific gravity, which is found to reach 21,061. It is ductile and malleable ; its hardness and tenacity are greater than those of gold, and it admits of being welded.
Silver is a noble metal, of a white color whose specific gravity is variable from 1O,474 to 10,542 ; it is very malleable and ductile, and of a moderate hardness. It fuses in a heat of less intensity than is required by gold ; it is fixed in fire, and is not affected by water nor air, remaining in both unaltered ; but by sulphureous vapours it is very soon tarnished.
Mercury, or quicksilver is a base metal of a white colour. Its specific gravity is upon an average 13,674 — it is the most fusible of all known metals, and continues in the fluid state even in the cold temper- ature of our winters j it congeals only at
1 70 Fossils.
40 Farenheit, and shews then some tena- city and ductility.
Lead is a base metal of a bluish white colour. Its specific gravity is from 11,- 352 to 11,445 ; it is considerably ductile but little tenacious and hard, hence it may be extended in thin plates by the hammer but not drawn into fine wire. It has scarcely any elasticity.
Bismuth is a yellowish or reddish white metal, of a foliated fracture, and very brittle, it being even reducible to powder by the hammer. Its specific gravity is from 9,670 to 9,822. It is somewhat harder than lead but more fusible.
Nickel is a greyish white metal, of a specific gravity between 9,OOO and 9,333 It is malleable, and very compact or firm.
Copper is a base metal, of a brownish red colour ; sonorous, very tenacious, ductile, and malleable ; of a considerable compactness ; of a moderate hardness and elasticity ; and of an hackly fracture. Its specific gravity varies from 7,788 to 9,000.
Arsenic is a brittle metal, and on the recent fracture, of a mean colour, betwixt tin- white and lead-grey ; but, on expo-
Fossils. in
sure to air, it soon turns black and dull. Its specific gravity is 8,310; its hardness is somewhat considerable, and seemingly surpassing that of copper. But its duc- tility is so little, and its brittleness so great that it is readily converted into powder by the hammer.
Of all metals Iron exhibits the most varieties and deviations. Its differences in colour, density, fracture, tenacity, duc- tility, and degree of fusibility, are uncom- monly great. — Soft and malleable iron has a greyish-white^ colour, a light grey, fi- brous,hackly fracture. Its specific gravity at a mean rate is 7,700 ; its hardness is not great, but its malleability and tenaci- ty are considerably so ; and it has this characteristic property, not possessed by other species of this metal, that whether cold or ignited, it may be extended, forg- ed, and bent, without breaking.
By cast or crude iron, that metal is understood, which is obtained by the first smelting of iron-ores. Such iron is distinguished from ductile iron by its re- fusing to be extended and forged by the hammer, whether cold or ignited, by its brittleness ,aud by its fusing in strong heat
172 Fossils.
in open fire, without addition, whereby it is rendered capable of being cast into moulds. The colour of crude iron is more or less of a pale grey.
Steel differs from both the ductile and the crude iron. — Its distinguishing pro- perty is, that when it is tempered^ that is to say, when it is hastily plunged in cold water while ignited to redness, it be- comes harder, more brittle, and inflexi- ble ; and that, before this tempering or hardening, it is ductile, whether cold or ignited ; and also, that after having been hardened, it reassumes its ductility by a fresh igniton and gradual cooling, with- out quenching. — Its colour is a light grey, its fracture finely granular.
Cobalt is a base metal, of a lead grey colour, brittle and hard, and of specific gravity from 7,000 to 7,700. This metal is rather of difficult fusion.
Tin is a base metal of a white colour, a little more verging to blue than that of silven — -It is very soft, pretty malleable and tractable ; its compactness and elas- ticity are but slight. When broken or bent, or when compressed betwen the teeth, it makes a peculiar crackling noise7
Fossils* 173
which is one of its characteristic proper-* toes. The specific gravity of tin is varia- ble from 7,216 to 7,331. Its gravity de- creases in the ratio of its purity.
Zinc is a white metal, of a radiated texture, changing into the foliated* It is of a middle kind betwen the malleable and brittle metals, and may be extended into thin laminae, at least between metal- lic cylinders in rolling mills. The spe- cific gravity of this metal is from 6,862
Antimony has a white colour, resem- bling that of tin, a foliated radiated text- ure, and is very brittle. Its specific gra- vity varies from 6,702 to 6,860. In the air it loses little of its metallic splendour and it does hot rust in the strict sense of the word.
Manganese is a white, hard, brittle me- tal, whose specific gravity is found to be from 6,850 to 7,OOO.
Molybdena has a pale lead-grey colour, a metallic lustre, and a laraellated fracture it is very soft, and marks paper easily, leaving a shining trace. Its specific gra- vity is between 4,138 and 4,569.
Wolfram is a metallic substance of modr P
Fossil*.
ern discovery, and of a particular kind, whose calx or oxyd is of a yellow colour, and one of the constituent parts of the fos- sil, called tungsten.
Another distinct metallic substance on- ly a few years since discovered by Klap- roth, is the Uranium. The oxyd of u- ranium has a lemon-yellow colour, is fix- ed in fire, and infusible when alone. Ig- nition changes its colour to a brownish grey.
We are likewise indebted to Klaproth for the discovery of the new metal called by him Titanium or Titanite. — It is con- tained in the mineral called red shoerl as a native oxyd. The colour of the perfect oxyd of titanium is red ; but when kept In violent ignition upon coals, and by a greater degree of disoxydation, it gradu- ally assumes a yellowish, bluish, and blackish hue.
Tellurium is a metal of a white colour like tin, inclining to lead-grey. It is brittle and friable ; possesses a lamellar texture, and considerable metallic lustre ; is one of the most easily fusible metals, and ex- hibits a crystallized surface when slowly cooling after fusion.—- Its specific gravity is 6,1 15.
fossils. 175
Chrome is a white metal, inclining to grey, very brittle, and crystallizable at an elevated temperature in feathered fila- ments on the surface.
The minerals to be found in England are both curious and useful. Amber, jety vitriol and allum are found in considera- ble quantities ; our canal coal approaches nearly to the beauty of jet, and even our common coal fire for firing is of a superior nature. The English earth and gravel are of the best quality; and we have stone,, slates, flags, and other fossils necessary for building in great abundance. Tin is another article in which England, from the time of the Phenicians had always had the pre-eminence- The county of Corn- wall alone produces more than all the world besides. Our lead ore is richer than in other countries, runs more fluently in the fire, require^ less trouble and ex- pense in working, and is when wrought very fine and ductile* Our black lead or wadd, found in Cumberland, is a mineral of great use and value in several branches of trade and arts. Copper and iron are also found here in great plenty, and seve*
176
Fossils.
ral ores of these metals, particularly in Anglesey, have of late been discovered, and brought into use, which were un- known before the recent improvements in chemistry.
Plants*
. X.
Of Vegetables or Plants
NEXT to the earth itself, we may con- sider those that are maintained on its surface ; which though they are fastened to it, yet are very distinct from it : and those are the whole tribe of vegetables or plants. These may be divided into three sorts, herbs, shrubs^ and trees.
Herbs are those plants, whose stalks are soft, and have nothing woody in them, as grass, sowthistle, and hemlock. Shrubs and trees have all wood in them ; but with this difference, that shrubs grow not to the height of trees, and usually spread into branches near the surface of the earth ; whereas trees generally shoot up in one great stem or body, and then, at a good distance from the earth, spread into branches ; thus, gooseberries and currants, are shrubs ; oaks and cherries, are trees.
P2
Plants.
Numerous are the works which have been written, especially in later times, on the science -of botany, and various sys- tems, or classifications of plants have from time to time been proposed; but the sexual system of Linnaeus is at pre- sent generally received. This naturalist has cjrawn a continued analogy between the vegetable economy and that of the animal ; and has derived all his classes, orders, and genera, from the number, situation, and proportion of the parts ot fructification. In twenty-four classes, he has comprehended every known genus and species. In considering a plant with a view to its characteristics, or dis- tinguishing features, it is divided by Lin- naeus into the following parts, making so many outlines, to which the attention o£ the botanical observer must be directed ; 1. Root ; 2. Trunk ; 3. Leaves ; 4. Props 5. Fructification ; 6. Inflorescence. 1* The root consists of two parts, the caudex and the radicula. The caudex, or stump, is the body or knob of the root from which the trunk and branches ascend, and the fibrous roots descend, and is either solid, bulbous, or tuberous 5 solid, as in trees*
Plants. 179
and other examples ; bulbous, as in tulips &c. tuberous, as in potatoes, &c. The radicula is the fibrous part of the root, branching from the caudex. 2. The trunk, •which includes the branches, is that part which rises immediately from t\ir caudex in either herbaceous, shrubby, or arbor- escent, and admits of several other dis- tinct! ons,according to its shape,substance, surface, &?c. 3. The leaves are either sirs pie, as those that adhere to the branch singly, or compound, as when several ex- pand from one footstalk. Leaves are far- ther described by various terms indicative of their form and outline. 4. The props those external parts which strengthen support, or defend, the plants on which they are found, or serve to facilitate some necessary secretion ; as the petlious, or footstalk of the leaf; the pedunculus, or footstalk of the flower, the stipula, or husk, that is, the small leaves that gener- ally surround the stalk at its divisions ; the cirrfiU8,or tendril; ihepubes, or down; the arma, or defensive weapon, as thorns* 5. The fructification, or mode, of fruit- bearing. 6. The inflorescence, or mode by which the flowers are joined to the seve- ral peduncles.
180 Plants.
In plants there is an infinite diversity; some aquire a long succession of ages to bring them to perfection, while others at- tain their full maturity in a few hours ; some are of immense magnitude, while others are of an inferior stature, descend- ing by gradation till they become too mi- nute to be cognizable by the senses. The mighty baobob of Senegal, described by Adanson,whose stem is 75 feet in circum- ferance, stands a stately monument on the face of the earth for many thousands of years ; while the mushroom, which it much resembles in form, springs up in a day, perfects its seeds, and is withered to- morrow ; and when we carry our views still farther, into that immense profound of minuteness which has but of late been partly laid open to us by the invention of the microscope ; into the class of mosses, which are in some measure cognizable by the naked eye, and still farther into the more minute class of plants denominated mould, which, even in those of the largest species, are too small to have their parts cognizable by the naked eye, and which, when viewed by the best microscopes, discover a series of existences diminish
Plants. 181
ing by a regular gradation, like stars in the galaxy under the best telescopes, till they are lost in the infinity of minuteness, leaving every reason to believe, that, could the magnifying powers of our in- struments be augmented a thousand fold, we should still find ourselves as far from discovering the termination of this series of infinite diminution as we were at the commencement of our imperfect survey. The world that we see, therefore, seems to be but a very small part of that which exists ; our feeble optics are capable of taking in scarcely a point of that universe which surrounds us ; and our imperfect understandings can scarcely obtain a glimpse of that infinite power and wisdom which regulates the whole. Among this infinity of objects, however, we can clear- ly perceive the most perfect regularity and order pervading every part; and that all the operations of nature proceed with invariable steadiness to effect the purposes for which they have been de- signed.
Thus we see that all animate objects, from the largest that has been discovered on this globe, to the smallest that can
182 Plants.
ever be made to be perceptible to us, in- variably proceed from other animated ob- jects of the same kind, although they ap- pear at times under such disguised forms as not to be at first sight cognizable by us. This rule applies to vegetables as well as animals. The plant of mould, which, even when it hath attained its full stature, can scarcely be perceived as a point under our microscopes of the highest magnify- ing power, we have every reason to be satisfied, produces its seeds in as regu- lar order, which ripen at their appointed period with the same regularity as those of the mighty baobob ; but while this re- mains a stately monument upon the sur- face of this earth, and sees thousands of generations of men succeed each other, and successively shelter themselves un- der the protecting shade of its spreading branches, we observe the mould spring up, perfect its seeds, scatter them in imper- ceptible myriads in the air, and disap- pear within the short space of one hour : so that during the short period of our existence here many myriads of genera- tions of mould have succeeded each other. Time itself then, when the universe is
Plants. 183
viewed as a whole, can only be consider- ed as a relative object. Shall man then, a being who cannot comprehend fully the nature of a single object around him, dare proudly to lift up his face, and pre- tend to decide concerning possibilities and the powers of nature ! His proper province is to be humble and adore !
The plants with which we are best ac- quainted may be arranged into three grand divisions. The first are those whose roots and stems remain for many years, which comprehends all the varie- ties of trees and shrubs. These, for the most part, require several years to bring them to a state of puberty (if that phrase may be admitted)^ when they begin to put forth flowers, and perfect their seeds ; after which time they usually continue to produce an annual crop of flowers and seeds for a long period of time ; the fruit in general succeeding the flowers, and perfecting their seeds in the same year ; but to this rule there are several excep- tions. In a few instances the seeds do not attain to muturity in the same sea- son that the flower is produced ; but? continuing upon the tree the whole win*
184 Plants.
ter in an immature state without being killed, they advance in the second season, and then only perfect their seeds; instances of which are to be found in the juniper and orange-tree. Others continue to ad- vance for several years, as usual, with- out showing fruits ; and when at length they reach that state of maturity, they then flower, and, having perfected their seeds, they decay and flower no more, dying down like annual plants ; an exam- ple of which is to be found in the cab- bage-tree of tropical regions. Some are scarcely ever (perhaps never) known to produce either flowers or seeds of any sort, but admit of being propagated by some other means ; instances of which are to be found in the English elm of our own country, the jack, or bread-fruit tree of India ; and many others.
The second division of plants are- those that have a perennial root, from which stalks are sent forth annually, which us- ually produce flowers, perfect their seeds in the summer, and die down to the ground at the approach of winter. The stems of these are for the most part of a similar structure and consistence with those of
Plants. 18*
The third class, or annuals, from the seeds of which, if sown in the spring^ stalks spring up which produce flowers and seeds the same season ; after the perfecting of which the stalks decay and die entirely away. Biennials can only be viewed as a diversity of these, that have not sufficient length of season to bring them to perfection in one year.
Whether distinctions similar to these take place among those minute tribes of plants which we call microscopical, it exceeds our power at present to deter- mine. From the short period of their existence, we have been generally in- clined to think that they are all similar in quality to annuals ; that is to say, that