CHAPTER II

OF THE HEAVENLY BODIES IN PARTICULAR

The sun is apparently the most magnificent and splendid orb in the heavens. And the most obvious phenomena attending it, are its light, its heat, and its daily rising and setting; but although the sun appears extremely bright and splendid to the naked eye, yet he is frequently observed even through a telescope of very moderate powers, to have dark spots on his disk. These were first discovered in 1611 : and the honour of the discovery was disputed between Galileo and Scheiner a German jesuit of Ingolstadt.

There is a great variety in the magnitude of these spots. The dif­ference is chiefly in superficial extent of length and breadth ; their depth or thickness is very small; some have been computed to be so large, as to be capable of covering the continents of Asia, and Africa, and even of the globe itself. The diameter of a spot, when near the middle of the disk is measured by comparing the time it takes in pas­sing of a hair, laid across the telescope, with the time it takes the whole disk to pass over the same hair; it may also be measured by a micrometer. By either of these methods, we may judge how many times the diameter of the spot is contained in the diameter of the sun.

It is observed that these spots are subject to increase and diminution of their magnitude, that they are of various shapes, most of them having a deep black nucleus surrounded by a dusky cloud, whereof the inner parts near the black are a little brighter than the out-skirts. They frequently change their shapes in the manner of our clouds, though not often so suddenly: thus what is of a certain figure to-day, tomorrow, or perhaps in a few hours shall be of a different one ; one spot is sometimes broken into two or three, and sometimes two or three spots shall coalesce, and be united in one. The number of spots is very uncertain, sometimes there are a great many, sometimes very few; and sometimes none at all.

It is evident from the various appearances, that the spots are not endowed with any permanency, nor are they uniform in shape, number magnitude, or duration. Hevelius observed one that arose and vanished in 16 or 17 hours; and no one has been observed to con­tinue longer than 70 days; in general those spots which are gradually formed, are gradually dissolved; and those which appear suddenly, are suddenly dissipated; it has been observed that when a spot disappears, the particular place which it occupied becomes brighter, on the other band those parts called faculae frequently turn to spots.

The sun when free from spots, appears equally luminous to the eye, or through coloured glasses. But through a telescope, the middle of the disk appears brighter than the out-skirts, the light darting more directly to us from the middle than the other parts, and the faculae appear more distinctly near the sides.

The spots are not confined to one part of the sun’s disk; though we have not heard of any being observed about his polar regions. They described different courses over the sun’s disk, sometimes they travel in straight lines, sometimes in curves; sometimes descending from the northern to the southern part of the disk, sometimes ascending from the southern to the northern, &c. Besides these spots there are others which sometimes appear very round and black, travelling over the sun’s disk in a few hours, and are totally unlike the others. These proceed from the interposition of the planets, Mercury, and Venus, between the earth and the sun. Excepting these two kinds of spots, nothing is discoverable on the surface of the sun, but he appears like an immense ocean of light.

Mr. Huygene supposed the sun to be a liquid globe, which the equal distribution of its rays, he thought was an argument for. The small inequalities upon it discovered by means of the telescope, and which has made some imagine they saw huge mountains of fire, he considered as entirely owing to the trembling motions of the vapours of our atmosphere; and that it was likewise the cause of the twinkling of the stars; and indeed it is not much to be doubted but that our vision is abundantly, more affected by the medium of our own atmosphere than we are aware of For instance, should we deviate ever so little from the old established hypothesis, that light travels in straight lines, and should it hereafter be discovered, that the motion of light, like all other motion, is elliptical, it would very materially affect our calcula­tions of the distances, magnitudes, and appearances of the celestial bodies.

When the moon passes between the earth and the sun, so as to intercept his rays, he is said to be eclipsed. This happens only at the time of new moon, because it is then only she passes between the sun and the earth. Yet the sun is not eclipsed at every new moon, because the moon more frequently declines from a straight line between the earth and the sun, either to the north, or the south. And this is also the case when the moon passes at the opposite conjunc­tion, when she passes to the northward or southward of the earth’s shadows.

No solar eclipse can be universal, the moon being too small to over­shadow the whole earth. Consequently the eclipses of the sun do not appear the same in all places, but are total in one, and partial in another. In most solar eclipses the moon is covered with a faint dawning light, which appears owing to the reflection of the light from the illuminated parts of the earth. In total eclipses, the moon’s edge is seen sur­rounded by a pale circle of light, which is at least a probable indication. of a lunar atmosphere.

When the earth is interposed between the moon and the sun in a direct line, so as to intercept his rays upon the moon, then the moon is eclipsed. And this is only at the time of the full moon. In the midst of a lunar eclipse the moon is observed to have a faint light, which is supposed to be reflected by the’ atmosphere of the earth, and that to the shadow of this it is owing, that she grows paler and dimmer before she enters into the shadow of the earth.

The interior conjunction of the planets, Mercury, and Venus, when passing over the sun’s disk, are not called eclipses, but transits.

The greatest diameter of the sun as seen from the earth is 32’ 36’, or 883,217 miles. It is stated from observations to revolve on its own axis in 25h. 15’ 16”, and is computed to be 1,380,000 times larger than the earth. It has been calculated to be 97,000,000 of miles distant from our earth.

2. Mercury to our observation at least, is the nearest planet t. the sun; this planet when viewed through a telescope magnifying about 200 or 300 times, appears equally luminous throughout his whole surface, without the least spot. He exhibits the same phases with the moon, being sometimes horned, sometimes gibbous, and sometimes shining with a full face, though not entirely full, because his enlightened side is never turned directly towards us, but at all times perfectly well defined, without any ragged edge and perfectly bright.

This planet performs its entire revolution in its orbit, in 87 days, 23 hours, and 15 1/4 minutes, which of course is the length of its year. Its distance from the sun is computed to be 27,000,000 of miles, or as have computed it to be 1/4 the distance of the earth. Its greatest apparent diameter as seen. from the earth 11”, or 3222 miles. ‘Its diurnal rotation is unknown, it not being possible from appearance on his disk, to come at a knowledge of his rotary mo­tion. - The inclination of his orbit to the ecliptic, is 70; its bulk is (thpnted to be of that of our earth, and its proportion of density 2-1, and its light 6-I.

3.Venus is next to Mercury, and the second interior planet it is rarely seen to shine with a full face, but has phases and changes like those of the moon, her illuminated hemisphere being constantly turned towards the sun. This planet is what is termed the morning and evening star, as she is situated in different parts of her orbit.

Dr. Herschel has published in the philosophical transactions for 1793, a long series of observations on this planet, whence he con­cludes, that the planet revolves about its axis, but that the period, and position of the axis are uncertain, that it has a very considerable atmosphere; that it exhibits inequalities of surface, though he could not discover much of them; owing probably to the density of its atmosphere; and that this planet instead of being smaller, is some­what larger than the earth; though former astronomers have computed its diameter at 7687 miles, which is 275 miles less than the diameter of the earth, or its bulk of the’ earth; and its diurnal rota­tion to be 23h. 22’. Its mean distance from the sun, is computed to be 68,000,000 of miles.

The earth as a planet, offers itself next to our contemplation, as being situated next in order in the solar system. But as it involves phenomena, and considerations abundantly more numerous and inte­resting than the surrounding orbs, we shall first take a brief survey of those celestial bodies, which occupy the remoter regions of space, and first of the exterior planets, Mars, Jupiter, Saturn, and Herschel.

4.Mars is the next planet; and is called an exterior planet, because it describes an orbit without the orbit of the earth. He is of a red, fiery colour, and gives a much duller light than Venus, though he sometimes equals her in size. He is not subject to the same limita­tions as Venus or Mercury, but appears sometimes very near the sun, and sometimes at a great distance from him. Sometimes rising when the sun sets, or setting when he rises. Mars appears gibbous when near his quadratures with the sun.

Much larger and more remarkable spots have been perceived on the disk of Mars, than on that of any other primary planet. By very accurate observations, Herschel has determined the proportion be­tween the polar and equatorial diameters, and the length of the day of this planet. He has also given some plausible conjectures on its and atmosphere; the latter it is now satisfactorily ascertained to have, though not to so great an extent, as conjectures on former observations led astronomers to imagine.

The mean distance of Mars from the sun is computed to be 144.000,000 of miles, its diameter 1189 miles. Its diurnal rotation, 24h, 39’ 22”, the inclination of its orbit to the elliptic, 10 51’. Its proportion of solar light, 43. Its bulk in proportion to the earth 7/10 And its proportion of density

5. Jupiter is the next exterior planet in the solar system., He has the same general appearance with Mars, only the belts on his surface are much larger, and more permanent. The number is very variable, sometimes being only one, at other times no fewer than eight may be perceived. They are generally parallel to one another, but not always so; and their breadth is likewise variable, one belt having been observed to grow narrower, while another in its neighbourhood has increased in breadth, as if the one had flowed into the other.

The time of their continuance is also uncertain. sometimes remaining unchanged for three months together, at others, new belts have been formed in an hour or two. In some of these belts large black spots have appeared, which moved briskly over the disk from east to west, and returned in a short time, to the same place; from whence the rotation of this planet abut its axis has been determined

The figure of Jupiter is evidently an oblate spheroid, the longest diameter of his disk being to that of the shortest as 13 to 12. Ills rota­tion is from west to east like that of the sun, and the plane of his equator is very nearly coincident with that of his orbit ; so that there can be very little difference of seasons in that planet. His rotation has been observed to be quicker in his aphelion than his perihelion.

The most remarkable circumstances attending this planet, is his having four moons or satellites, which constantly revolve round him at different distances. These are all supposed to remove in ellipses, though the eccentricities of all of them are too small to be measured, excepting that of the fourth, and even this amounts to no more than 0,007 of its mean distance from the primary.

The periodic times and distances of these satellites, in semi-diame­ters of Jupiter, and in English miles, the angles under which their orbits appear, as seen from the earth, at its mean distance from Jupiter, taken from the latest and most exact observations, are ‘as follows.

6. Saturn sometimes appears at a vast distance from the sun shines with a very faint light; and his motion is so slow among the fixed stars that unless carefully observed, he will scarcely be thought to move at all When viewed through a good telescope, he makes a more remarkable appearance than any of the other planets. Galileo first discovered his uncommon shape, and from his discoveries and those of other astronomers, it appears that this planet is surrounded by a broad ring, the edge of which reflect little or none of the sun’s light to us; but the planes of the ring reflect the light in the same as the planet itself does: the diameter of the ring is about the diameter of the body of the planet. The ring is detached from the body of the planet in such a manner, that the distance between the innermost ‘part of the ring and its body, is equal to its breadth.

Dr. Hershel has found in the course of observation, that the ring is double, or that there are two concentric rings; also that it has a motion of rotation in its own plane, its axis of motion being the same with that of Saturn himself, and its periodical time 10h 32’ 15”. 4 but he thinks it probable, that the concentric rings may not revolve in the same period. Their dimensions and the space between them, he states in the following proportions to each other.

Miles.

Inner diameter of the small ring, .. 146,345

Outward diameter of do. 184,393

Inner diameter of the large ring, 190,248

Outside diameter of do. 204,883

Breadth of the inner do. 20,000

Breadth of the outer do. 7,200

Breadth of the vacant space 2,839

Dr. Herschel concludes from his observations on the ring, that its structure is such, as to alLow it to remain permanently in its present state; nor does he think it at all probable, that the ring is of that changeable nature which some have imagined.

The same excellent astronomer has concluded from a series of observations on the belts of Saturn, that he revolves on his axis in 10h. 16' 0”.4, that be has a dense atmosphere, and that his polar diameter is to his equatorial as 10 to 11.

Saturn has, besides his ring, seven secondary planets or satellites revolving round him. One of them, which till lately was reckoned the fourth in order from Saturn, was discovered by Huygens, in 1655, and by means of a telescope of 100 feet long; and the others; viz. the 1st, 3d 4th., and 5th. at different times by Cassini, between 1671 and and 1684, by the help of glasses of 100 and 136 feet. The 6tband 7th have been lately discovered by Herschel, with his 40 feet reflecting telescope in 1787 and 1788. These he has called the 6th and 7th satellites, though they are nearer to Saturn than the other 5, that the names may not be mistaken with regard to former observations of them.

The periodical revolutions and distances of these satellites ex. pressed in semi-diameters of that planet, and in English miles, are as follows.

The 4 first described ellipses like those of the ring, are in the same plane: their inclination to the orbit, is from 300 to 31°. The 5th describes an orbit inclined from 17° to 18° to the orbit of Saturn, his plane lying between the ecliptic and those of the other satellites. Dr. Herschel observes that the 5th satellite turns round its axis once, exactly in the time in which it revolves round the planet Saturn. In this respect it resembles our moon, which does the same thing.

7. The Georgium Sidus, or Herschel, being more remote than Saturn, is also less known. Its apparent magnitude is so small, that it can seldom be seen by the naked eye, and even when viewed by means of the telescope, it appears only a few seconds in diameter. This planet was discovered by Dr. Herschel, in 1781; and in 1787 he likewise discovered two satellites that revolve round it. They are probably not less than Jupiter’s moons, and their orbits are nearly perpendicular to the ecliptic. This is a circumstance in which they differ from the attendants of all the other planets.

Their periods of revolution and angular distances from their primary, are as follows.

8. Comets are another class of planets appertaining to our system, and which exhibit appearances vastly different from any of the other planets. The nucleus or star, seems much dimmer; they are to appearance surrounded with atmospheres of a prodigious size, often rising ten times higher than the nucleus, and often likewise exhibit different phases, like the moon.

What is called the head of a comet, or the round part, appears to be a solid globe, and is called the nucleus, which is easily distinguished from the atmosphere of hairy appearance.

Comets are peculiarly distinguished by a blaze or tail, also by the eccentricity of their motion. Sometimes the tail only has been seen at ‘the head has been hid under the horizon, then it is termed a beam. There appears to be a relative degree of conformity peculiar shape of the atmosphere of comets, the velocity with which they move, and the extreme ellipsis in which they traverse. None of the celestial bodies have given rise to a greater degree of speculation and conjecture than the comets. Their strange appear­ance has in all ages been a matter of terror to the vulgar, who uni­formly looked upon them as bad omens, or forerunners of war, pesti­lence, &c. Others less superstitious, have supposed them to be meteors formed in the upper regions of the air. After much specu­lation and conjecture among astronomers, Tycho Brahe restored them to their true rank in the creation, and Sir Isaac Newton at length discovered their true motion, from the observations he made on the great comet which appeared in 1680 This comet appeared to descend almost perpendicular towards the sun with a prodigious velo­city; ascending again with a motion retarded as much as it had been before accelerated. It was seen in the morning by a great number of astronomers in different parts of Europe from the 4th to the 25^th of November, in its way towards the sun, and in the evening, from the 12th of December to the 9th of March following. The many exact observations made on this comet, enabled Sir Isaac Newton to deter-mine, that they are a kind of planets, which move in very eccentric ellipses and this opinion is now considered as an established truth. Although the orbits of all comets are very eccentric ellipses, yet there ‘are very great differences among them. Excepting the orbit of Mercury there are no great differences among those of the planets, either as to their eccentricity, or the inclination of their planes; but the planes of some comets are almost perpendicular to others, and. some of their ellipses are much wider than others. The narrowest. ellipsis of any comet hitherto observed, was that of 1680. There is also a much greater inequality in the motion of the comets, than in the planets; the velocity of the former being incomparably greater in their perihelion than in their aphelion; but the planets are but little accelerated. Hence it is apparent, that the degree of acceleration of any orb, will be in a ratio proportionate to the degree of the ellipsis of its orbit ; for it is evident from all observation, that a body is retarded in its aphelion, in a degree corresponding to its acceleration in its perihelion distance.

It is now universally allowed that comets are opaque bodies, enlightened by the sun. Sir Isaac Newton observes that if a comet be observed, in two parts of its orbit at equal distances from the earth, but at unequal distances from the sun, it always shines brightest in that part which is nearest to the sun.

Comets are of very different magnitudes, which may be observed from their apparent diameters and brightness.

The extraordinary atmospheres, or tails of comets, have given rise to various conjectures, though it is allowed by all, that they depend on the sun some way or other, as they are always directed towards him in one undeviating position; but by what means this is effected is a subject of dispute among philosophers.

The analogy discovered by that indefatigable astronomer, Kepler between the periodical times of the planets, and their distances from the sun, takes place also in the comets. In consequence this, the mean distance of a comet from the sun, may be found by comparing its period with the time of the revolution round the sun. Thus the period of the comet which appeared in 1531, ,IeOI, I68 and 1759 being about 76 years, and whose regular return will be about the year 1835, its mean distance may be found by the following proportion. As I, the square of one year, the earth’s periodical time, is to 5776, the square of 76, the comet’s periodical time, so is 1,000,000, the cube of 100, the earth’s mean distance from the sun, to 5,77,000,000, the cube of the comet’s mean distance. The root of this last number

1794, the mean distance itself in such parts as the mean distance of the earth from the sun contains 100. If the perihelion distance of the comet 58, be taken from 3588, double the mean distance, we shall have the aphelion distance 3530, of such parts as the distance of the earth contains 100, which is a little more than 35 times the distance of the earth from the sun. By a like method, the aphelion distance of the comet of 1680, comes out 138 times the mean distance of the earth from the sun, supposing its period 575 years ; so that this comet in its aphelion goes more than 14 times the distance from the sun that Saturn does. Euler computes the orbit from three of Flamstead’s observations, taken nearly together, compared with a fourth, taken at some distance from the other three, and from thence concludes the.-period to be a little more than 170 years.

9.The next celestial objects which present themselves in succession to our notice, are those innumerable orbs, which we term fixed stars: they are termed fixed, because they appear not to vary their situations in the heavens, to a spectator on the earth. Astronomers have supposed them to be so many suns, each the centre of a system of habitable worlds, similar to our solar system. The strongest argu­ment for this, is, that the stars cannot be magnified, even by the most powerful telescope, on account of their immense distance; whence it is concluded, that they shine by their own light, and are therefore so many suns; each of which we may suppose is of equal if not superior magnitude to our own. They are situated at vastly different distances from us, as is indicated by their different magnitudes; and this supposition is necessary, to prevent any interference of the orbits of the planets, and thus there may be as great a distance between a ___ of the first magnitude and one of the second, apparently close to it, as between our globe and the fixed stars themselves.

The fixed stars, instead of being magnified by the best glasses, are ___ diminished in size, on account, as is thought, that the telescope takes off that twinkling appearance which they exhibit to the naked eye., or more probably, that the rays being very much compounded in consequence of their immense passage, the superfluous rays are excluded by the instrument; and this is inferable from the fact, that the number of stars is prodigiously increased by the telescope, 70 stars having been counted in the single constellation Pleiades, and fewer than 2000 in that of Orion.

The late great discoveries and improvements of the celebrated Herschel have thrown new light on this subject, and shown the number of stars to be exceedingly beyond the discoveries, and even the apprehensions of the ancients. This able astronomer has shown that many which appear single to the naked eye, or through ordinary glasses, do in fact consist of two or more stars; and that the galaxy or milky way, owes its light entirely to multitudes of small stars, so close together, that the naked eye, or even ordinary telescopes cannot distinguish them.

The nebulae, or small whitish specks, discoverable by means of the telescope, in various parts of the heavens, are owing to the same cause. Former astronomers could only reckon 103 of these nebulous patches, but Herschel has discovered upwards of 1250. He has also discovered a species of them which he calls planetary nebulae, on account of their peculiar brightness, and their shining with a well defined disk.

In the philosophical transactions for 1783, Mr. Mitchell, in proposing a method to determine the distance, magnitude, &c. of the fixed stars, by the dimmution of the velocity of their light, should any such thing be discovered, supposes, that by far the greater par, if not all of them, are systems of stars, so near to each other, as probably to be liable to be affected sensibly by mutual gravitation; and that it is therefore not unlikely that the periods of the revolutions of some of these about their primaries, the smaller ones being upon this hypothesis to be considered as satellites to the other,) may at some time or other be discovered. Dr. Herschel, improving upon Mitchell’s idea, of the fixed stars being collected into groups, and assisted by his own observations, aided by his extraordinary telescopic powers, has suggested a theory concerning the construction of the universe, entirely novel and singular. The opinion had long prevailed among astronomers, that our sun, besides occupying the center of the system which properly belongs to him, occupied also the center of the universe; but Dr. Herschel is of a different opinion; we shall extract some of the doctor’s observations on this interesting subject.

Hitherto (says the Dr.) the siderial heavens have, not inadequately for the purpose designed, been represented by the concave surface of a sphere, in the centre of which the eye of the observer might be supposed to be placed. It is true, the various magnitudes of the fixed stars even then, plainly suggested to us, and would have better suited, the idea of an expanded firmament of three dimensions; but the observations upon which I am now going to enter, still farther illus­trate and enforce the necessity of considering the heavens in this point of view. In future, therefore, we shall look upon these regions, into which we may now penetrate by means of the improved telescopes, as a naturalist regards a rich extent of ground or chain of mountains, containing strata variously inclined and directed, as well as consisting of very different materials. A surface of a globe, or a map, therefore, will but ill delineate the interior parts of the heavens.”

The doctor’s observations, on which this theory is founded, were made with a Newtonian reflector of 20 feet focal length, and an aper­ture of 18 inches. With this powerful telescope, he first began to survey the Via Lactea, and found that it completely resolved the whitish appearance into stars, which the telescopes he formerly used, had not light enough to do. The portion he first observed, was about the hand and club of Orion; in which he found, an astonishing multi­tude of stars, the number of which he endeavoured to estimate, by counting many fields, (or apparent spaces of the heavens, which he could see at once through his telescope,) and computing from a medium of these, how many might be contained in a given portion of the milky way. In the most vacant place to be met with in that neigh­bourhood, he found 63 stars: other six fields, contained 110, 66, 70, 90, 70, and 74 stars, a medium of all which gave 79 for the number of stars to each field.—Thus he found that by allowing 15’ for the diame­ter of his field of view, a belt of 15° long, and 2 broad, which lie had often seen pass before his telescope, in an hour’s time, could not con­tain less than 50,000 stars, large enough to be distinctly numbered besides which, he suspected twice as many more, which could be seen only now and then, by faint glimpses, for want of sufficient light.

The doctor’s success thus far, soon induced him to direct his atten­tion to the nebulous parts of the heavens, of which an accurate list was published in the Connoissance de Temps for 1 783 and 1784. Most of these yielded to a Newtonian reflector of 20 feet focal distance, and 12 inches aperture, which plainly discovered them to be composed of stars, or at least to contain stars, and to show every other indication of consisting of them entirely.

“The nebulae (says he) are arranged into strata, and run on to a great length; and some of them I have been able to pursue and to guess pretty well at their form and direction. It is probable enough, that they may surround the whole starry sphere of the heavens, not unlike the milky way, which undoubtedly it nothing but a stratum of fixed stars; and as this latter immense starry bed, is not of equal breadth and lustre in every part, nor runs on in one straight direction, but is curved, and even divided into two streams, along a very conside­rable portion of it. We may likewise expect the greatest variety in the strata of the clusters of stars and nebulae.

“One of the nebulous beds is so rich, that in passing through a section of t in the time of only 36 minutes, no less than 31 nebulae have been detected, all distinctly visible on a fine blue sky. Their situation and shape, as well as condition, seem to denote the great­est variety imaginable. In another stratum or perhaps a branch of the former, I have often seen double and treble nebulae variously arranged; large ones with small seeming attendants ; narrow but much extended lucid nebulae or bright dashes; some of the shape of a fan resembling an electric brush issuing from a lucid point; others of a comatic shape, with a seeming nucleus in the centre, or like cloudy stars, surrounded by a nebulous atmosphere: a different sort again, contain a nebulosity of the milky kind, like that wonderful inex­plicable phenomenon about Orion is while others shine with a fainter mottled kind of light, which denotes their being resolvable into stars.

“It is very probable that the great stratum called the milky way, is that in which the sun is placed, though perhaps not in the very centre of its thickness. This we gather from the appearance of the galaxy, which seems to encompass the whole heavens, as it certainly must do, if the sun is within the same. For suppose a number of stars arranged between parallel planes indefinitely every way, but at a given considerable distance from one another, and calling this a siderial stratum; an eye placed somewhere within it, will set all the stars in the direction of the planes of the stratum, projected into a great circle, which will appear lucid on account of the accumulation of the stars, while the’ rest of the heavens at the sides, will only seem to be scattered over with constellations, more or less crowded, according to the distance of the planes, or number of stars contained in the thick­ness or sides of the stratum. If the eye were placed somewhere without the stratum at no great distance, the appearance of the stars within it, would assume the form of one of the lesser circles of a sphere, which would be more or less contracted to the distance of the eye; and if this distance were exceedingly increased, the whole stra­tum might at last be drawn together into a lucid spot of any shape, according to the position, length, and height of the stratum. Let us now suppose that a branch or smaller stratum should run out from the former in a certain direction, and let it also be contained between two parallel planes, extended indefinitely onwards, but so that the eye may be placed in the great stratum, somewhere before the separating and not far from the place where the strata are still united; then will the second stratum not be projected into a bright circle like then will former, but will be seen as a lucid branch proceeding from the first, and returning to it again at a certain distance less than a semicircle. What has been instanced in parallel planes may easily be applied to strata irregularly bounded, and running in various directions ; for their projection will of consequence vary, according to the quantities of the variations in the strata, and the distance of the eye from the same and thus any kind of curvatures, as well as various degrees of bright. ness, may he produced in the projections.

“From appearances, then, as I observed before, we may infer, the sun is most likely placed in one of the great strata of the fixed stars, and very probably not far from the place where some smaller stratum branches out from it. Such a supposition will satisfactorily and with great simplicity, account for all the phenomena of the milk way; which, according to this hypothesis, is no other than the appearance of the projection of the stars contained in this stratum, an its secondary branch. As a farther inducement to look on the galaxy in this point of view, let it be considered, that we can no longer doubt of its whitish appearance arising from the mixed lustre of the numberless stars that compose it. Now should we suppose it to be and irregular ring of stars, in the centre nearly of which we must suppose our sun to he placed, it will appear not a little extraordinary, that the sun being a fixed star like those which compose this imagined ring, should just be in the centre of such a multitude of celestial bodies without any apparent reason for this singular distinction; whereas on the other supposition, every star in this stratum, not very near the termination of its length or height, will be so placed as to have its own galaxy, with only such variations in the form and lustre of it, as it may arise from the particular situation of each star.”

A continued series of observations confirmed Dr. Herschel in these opinions; and in a succeeding paper, he has given a sketch of his ideas of the interior construction of the starry heavens.—” That the milky way (says he,) is a most extensive stratum of stars of various sizes, admits no longer of the least doubt; and that our sun is one of the heavenly bodies belonging to it, is equally evident. I have now viewed and gauged this shining zone in almost every direction, and find it composed of shining stars, whose number, by the account those gauges, constantly increases and decreases, in proportion to its apparent brightness to the naked eye.

“But in order to develope the ideas of the universe, that have been suggested by my late observations, it will be best to take the subject from a point of view at a considerable distance both of space then suppose numberless stars of various sizes and time. Let us then suppose numberless stars of various sized, scattered over an infinite space, in such a manner as to be almost divided through whole. The laws of attraction, which no doubt extend to the remotest regions of the fixed stars, will operate in such a manner most probably to produce the following remarka­ble effects.

1. It will frequently happen, that a star being considerably larger than its neighbouring ones, will attract them more than they will be attracted by others that are immediately around them; by which means they will be in time, as it were, condensed about a centre; or in other words form themselves into a cluster of stars of almost a globular figure, more or less regularly so according to the size and original distance of the surrounding stars. The perturbations of the mutual attractions must undoubtedly be very intricate, as we may comprehend, by considering what Sir Isaac Newton has said, (Princip. Lib i. Prob. 38. et seq.) but in order to apply this great author’s reasoning, of bodies moving in ellipses, to such as are here for a while supposed to have no other motion, than what their mutual gravity has imparted to them, we must suppose the conjugate axes of their ellipses indefinitely diminished, whereby the ellipses will become straight lines.

2. The next case which will happen almost as frequently as the former, is where a few stars, though not superior in size to the rest, may chance to be rather nearer each other than the surrounding one, for here also will be formed a prevailing attraction in the combined center of gravity of them all, which will occasion the neighbouring stars to draw together; not, indeed, so as to form a regular globular figure, but, however, in such a manner as to be condensed towards the common centre of gravity of the whole irregular cluster. And this construction admits of the utmost variety of shapes, according to the number and situation of the stars, which first gave rise to the condensation of the rest.

3. “From the composition and repeated conjunction of both the foregoing forms, a third may be derived: when many large stars, or combined small ones, are situated in long extended, regular, or crooked hooks, or branches; for they will also draw the surrounding ones, so as to produce figures of condensed stars coarsely similar to the former, which gave rise ~o these condensations.

4. ‘We may likewise admit of still more extensive-combinations; same time a cluster of stars are farming in one part of space, there may be another collecting in a different, but perhaps not The distant quarter, which may occasion a mutual approach towards this common centre of gravity.

5. “In the last place, as a natural consequence of the former cases, there will be great cavities, or vacancies, formed by the retreat of the stars towards the various centres which attract them; so that, upon the whole, there is evidently a field of the greatest variety for the mutual and combined attractions of the heavenly bodies to exert themselves in. .

“From this theoretical view of the heavens, which has been takes from a point not less distant in time than in space, we will now retreat to our own retired station, in one of the planets attending a star in great combination with numberless others; and in order to investigate) what will be the appearance from this contracted situation, let us begin with the naked eye. The stars of the first magnitude being in all probability the nearest, will furnish us with a step to begin our scale Setting off therefore, with the distance of Sirius or Arcturus, for instance as unity, we will at present suppose, that those of the second magnitude are at double, those of the third at treble the distance, &c. Taking it for granted then, that a star of the 7th magnitude (the smallest supposed visible with the naked eye) is about 7 times as far: as one of the first, it follows, that an observer, who is inclosed in a globular cluster of stars, and not far from the centre, will never be able with the naked eye to see the end of it; for since according to the above estimation, he can only extend - his view to about 7 times the distance of Sirius, it cannot be expected that his eyes should reach the borders of a cluster, which has perhaps not less than 50 stars in depth every where around him. The whole universe to him, therefore will be comprised in a set of constellations, richly ornamented with scat-tered stars of all sizes; or, if the united brightness of a neighbouring cluster of stars should, in a remarkable clear night reach his sight, it will put on the appearance of a small, faint, whitish, nebulous cloud, not. to be perceived without the greatest attention.

“Let us suppose him placed in a much extended stratum, or branching cluster of millions of stars, such as may fall under the third form, of nebulae already considered. Here also the heavens will not only be richly scattered over with brilliant constellations, but a shining zone, or milky way will be perceived to surround the whole sphere of the heavens, owing to the combined light of those stars which are too small, that is, too remote to be seen. Our observer’s sight will be 80 confined, that he will imagine this single collection of stars, though be does not even perceive the 1000th part of them to be the whole contents of the heavens.

Allowing him now the use of a common telescope, he begins to suspect that all the milkiness of the bright path which surrounds the sphere, may be owing to stars. He perceives a few clusters of them in various parts of the heavens, and finds also, that there are a kind of nebulous patches: but still his views are not so far extended as to reach the end of the stratum in which he is situated; so that he looks upon these patches as belonging to that system, which to him seems to comprehend every celestial object. He now increases his power of vision; himself to a close observation, finds that the milky way is indeed no other than a collection of very small stars. He perceives that those objects which had been called nebulas, are evidently nothing but clusters of stars. Their number increases upon him; anti when he resolves one nebulas into stars, he discovers ten new ones which lie cannot resolve He then forms the idea of immense strata of fixed stars, of clusters of stars, and of nebulas, till going on with such interesting observations, he now perceives that all these appearances must naturally arise from the confined situation in which we are placed. Confined it may justly be called, though in no less a space than what appeared before, to be the whole region of the fixed stars, but which now has assumed the shape of a crooked branching nebula; not indeed one of the least, but perhaps very far from being one of the most considerable, of those numberless clusters that enter into the construction of the heavens.”

Herschel shows, that this theoretical view of the heavens is perfectly consistent with facts, and seems to be confirmed by a series of observations. Many hundreds of nebulas of the first and second forms are to be seen in the heavens ; and their places, he says, will hereafter be pointed out; many of the 3d form described, and instances of the 4th related; a few of the cavities mentioned in the 5th par­ticularized, though many more have been already observed ; so that, upon the whole (says he) “ I believe it will be found, that the fore­going theoretical view, with all its consequential appearances, as seen by an eye inclosed in one of the nebulas, is no other than a drawing from nature, wherein the features of the original have e been closely copied: and I hope the resemblance will not be called a bad one, when it is considered how very limited must be the pencil of an inhabitant of so small and retired a portion of the infinite system, in attempting the picture of so unbounded an extent.”

The doctor having determined that the visible system of nature, by us called the Universe, consisting of all the celestial bodies, and many more than can be seen by the naked eye, is only a group of stars or suns, with their planets, constituting one of those patches called a nebula, and perhaps not one ten thousand millionth part of what is really the universe, he goes on to-delineate the figure of this vast nebula, which he is of opinion may now be done; and for this purpose, lie gives a table, calculating the distance of the stars which form its extreme boundaries, or the length of the visual ray in different parts, by the number of stars contained in the field of his telescope at dif­ferent times. He then proceeds to offer some thoughts on the origin of the nebulous strata of the heavens; in doing which, he gives some hints concerning the antiquity of them.

If it were possible (says he) to distinguish between the parts of a indefinitely extended whole, the nebulae we inhabit, might be said be one that has fewer marks of antiquity, than any of the rest. explain this idea, perhaps more clearly, we should recollect, that condensation of clusters of stars, has been ascribed to gradual approach and whoever reflects on the number of ages that must hive passed before some of the clusters that are to be found in my intended catalogue of them, could be so far condensed as we find them at present will not wonder if I ascribe a certain air of youth and vigour, to very regularly scattered regions of our siderial stratum. There are moreover, in my places in it, in which, if we may judge from appearances, there is the greatest reason to believe, that the stars are drawing towards secondary centres, and will in time separate into clusters so as to occasion many subdivisions.

“ Here we may surmise, that when a nebulous stratum consists chiefly of nebulas of the first and second forms, it probably owes origin to what may be called the decay of a great compound nebula of the third form ; and that the subdivisions which happened to it, it length of time occasioned all the small nebulas which sprung from it to lie in a certain range, according as they were detached from the primary one. In like manner, our system, after numbers of ages, may very possibly become divided, so as to give rise to a stratum of two or three hundred nebulas ; for it would not be difficult to point out so many beginning or gathering clusters in it. " This throws a considerable light, upon that remarkable collection of many hundreds of nebulas which are to be seen in what I have called the nebulous stratum in Coma Berenices. It appears from the extended and branching figure of our nebula, that there is room for the decomposed small nebulas, of a large, reduced, former great one, to approach nearer to us in the sides, than in any other part. Nay, possibly there might originally be another very large joining branch,-which in time became separated by the condensation of the stars: and this may be the reason of the little remaining breadth of our, system in that very place; for, the nebulas of the Coma are brightest and most crowded just opposite to our situation, or in the pole of the system.

“As soon as this idea was suggested, I tried also the opposite pole where, accordingly, I have met with a great number of nebulas, though under a much more scattered form. Some parts of our system, indeed, seem already to have sustained greater ravages of time than others; for instance, in the body of the Scorpion, in an opening which is probably owing to this cause. It is at least 4° broad; but its height I have not yet ascertained. It is remarkable, that the 80 Nebuleuse sans Etoiles of the Connoissance des Temps; which is also on the western border of another vacancy, and has, moreover, a small miniature cluster or easily resolvable nebula, of about 2 ½ minutes north. Following it at no very great distance.

There is a remarkable purity or clearness in the heavens, when we look out of our stratum at the sides ; that is towards Leo, Vergo, and Coma Berenices on the one band, and towards Cetus on the other;; where as the ground of the heavens becomes troubled as we approach towards the length or height of it. These troubled appearances are easily to be explained by ascribing them to some of the distant straggling stars ­that yield hardly light enough to be distinguished: and I have indeed, often experienced this to be the cause, by examining the spots for a long while together, when at last I generally perceived the stars which occasioned them. But, when we look towards the poles of our system, where the visual ray does not graze along the side the straggling stars will of course be very few in number; and therefore, the ground of the heavens will assume that purity which I have always observed to take place in those regions.”

The doctor here applies the name of poles to those points which are 90° distant from a circle passing along the milky way. The north poles is situated in R. As. 186° and distant from the pole of the world 58°.

According to Herschel, then, the universe consists of nebulas, or innumerable collections of innumerable stars, each individual of which is a sun, not only equal, but much superior to ours: and none of the celestial bodies in our nebulas are nearer to one another, than we are to Sirius, whose distance is supposed to be not less than 400,000 times that of the sun from us, or 38 millions of millions of miles. The whole extent of the nebulas being in some places near 500 times as great, must be such, that the light of a star placed at its extreme boundary, supposing It to fly with the velocity of 12 millions of miles every minute must, have taken near 3000 years to reach us. Hers­chel, however is by no means of opinion that our nebula is the most considerable in the universe.

“As we are used (continues he) to call the appearance of the heavens, where it is surrounded with a bright zone, the milky way, it may not be amiss to point out some other very remarkable nebulas, which cannot well be less, but are probably much larger, than our own system; and being also extended, the inhabitants of the planets

That attend the stars which compose them, must likewise perceive the same phenomena; for which reason they may also be called milky ways. For distinction’s sake. My opinion of their size is grounded on the following observations. There are many round nebulas of the first form, of about five or six minutes in diameter, the stars of which I can see very distinctly ; and on comparing them with the visual ray calculated from some of my long gauges, that the centres of these round nebula may be 600 times the distance of Sirius from us.”

He then tells us, that the stars in such nebulae, are probably twice as much condensed as those of our system: otherwise, the centre of it could not be less than 6000 times the distance that Sirius is from us; and that it is possibly much under-rated, by supposing it only 600 times the distance of that star.

“ Some of these round nebulas (says the Dr.) have others near ­them, perfectly similar in form, colour, and the distribution of stars, but of only half the diameter: and the stars in them seem to he doubly crowded, and only at about half the distance from each other. They are indeed so small, as not to he visible without the utmost attention. I suppose these nebulas to be double the distance of the first.

An instance equally remarkable and instructive is, a case-, where, in the neighbourhood of two such nebulas as have been mentioned, I met with a third similar, resolvable, but much smaller and fainter nebulas, the stars of it are no longer to be perceived, but a resemblance of colour with the former two, and its diminished size and light may well permit us to place it at full twice the distance of the first. And yet the nebulosity is not of the milky kind; nor is it so much as difficulty resolvable or colourless. Now in a few of the extended nebulas, the light changes gradually, so as from the resolva­ble to approach to the milky kind ; which appears to me an indication, that the milky light of nebulas is owing to their much greater distance. A nebula therefore, whose light is perfectly milky cannot well be supposed to be at less than 6000 or 8000 times the distance of Sirius; and though the numbers here assumed are not to be taken otherwise, than as very coarse estimates, yet an extended nebula, which an oblique situation, where it is possibly fore-shortened by one half, two thirds, or three fourths of its length, subtends a degree or more in diameter, cannot be otherwise than a wonderful magnitude. and may well out-vie our milky way in grandeur.”

After giving an account of several remarkable nebulas, Dr. Herschel concludes thus: “Now what great length of time must be required to produce these effects (the formation of nebulas) may easily be conceived, when, in all probability, our whole system, of about 800 stars in diameter, if it were seen at such a distance, that one end of it might assume the resolvable nebulosity, would not at the other end. present us with the irresolvable, much less with the colourless and milky nebulosities.” Great indeed must be the length of time, requi­site for such distant bodies to form combinations by the laws of attrac­tion, since, according to the distances. the Dr. has assumed, the light of some of his nebulas must be 36,00(J or 48,000 years in arriving from them to us. It would be worth while-then to inquire, whether attrac­tion is propagated in time or not, or whether it moves quicker or slower than light.

Several circumstances, however, lie says manifestly Lend to a gene­ral preservation. The indefinite extent of the siderial heavens must produce a balance, that will effectually secure all the great parts of the whole from approaching to each other. “There remains then (says he) only to see how the Particular stars belonging to separate clus­ters, are prevented from rushing on to their centres of attraction.” this he supposes may be done by projectile forces. “The admission of which will prove such a barrier against the seeming destructive power of attraction, as to secure from it, all the stars belonging to a cluster, if not for ever at least for millions of ages Besides, we ought perhaps to look upon such clusters, and the destruction of a star now and then in some thousands of ages, as the very means by which the whole is preserved and renewed. These clusters may be the laboratories of the universe, wherein the most salutary remedies for the decay of the whole are prepared.”

The existence of such projectile forces is rendered probable, from the apparent changes of position of certain stars, and from a compa­rison of the best modern observations, with the most accurate of former times, there appears to have been a real change in the places of some of them. The Bull’s Eye, Sirius, and Arcturus, are now found to be half a degree more southerly than the ancients reckoned them, and the bright star in the shoulder of Orion, has, in Ptolemy, almost a whole degree of latitude more southerly than at present. Dr. Herschel has lately observed that the distance and position of the two stars forming the double star, in Draconis, is different from what it was in Flamstead's time. So considerable is the change of distance (for it is 16".6) that he thinks we can hardly account for it otherwise, than by admitting a proper motion in the one or other of the stars or in our solar system; most probably he says, neither of the three are at rest.

If our solar system do really change its place in absolute space, in process -of time, an apparent change in the angular distances of some of the fixed stars will appear-; and the nearest being more affected than such as are more remote, their relative positions may be seen to alter, although the stars were really immoveable. and vice versa, we may surmise, from the observed motions of the stars, that our sun with all its planets and comets, may have a motion towards some particular part of the heavens, on account of a greater quantity of matter collected in a number of stars, and their surrounding planets there situa­ted, which may occasion a gravitation of our whole solar system towards it. On the other hand, if our system he at rest, and any of the stars really in motion, this might likewise vary their apparent posi­tion, and the more so, the nearer they are to us, or. the swifter their motions ‘are, or the more proper the direction of the motion is, to be rendered perceptible by us.

From this brief theoretical sketch, we derive an idea, which the ancient philosophy would not give us, of the amazing grandeur, mag­nificence, and sublimity of universal being: all the visible part of, which, is hut a mere speck, a comparatively little, branching fragment of the extended universe. And although it is impossible for us to attain to an identifying sensibility, and actual retrospect, in consequence of our limited situation, yet there is every reason to conclude, from analogy, observation, and reflection, that infinite space is thus occupied, and diversified, and that God is a God of the universe, and not merely of this little, straggling world of ours; which is but a little planet, attached to a single star, which appears somewhat eccentrized, from the -regular strata of worlds, and which we have been in the habit of contemplating, as of vast and superior magnitude.

It is a narrow, contracted, and local idea, that limits the boundaries of universal creation, to this little ball of earth, or this little solar system, of which we are a comparatively small member. The idea would appear more rational, and consistent, and more worthy of the munificent hand, that guides the stars in their courses, and grasps them in its palm, that could contemplate not only our own system, but the whole visible universe as a mere link of an infinitely extended system of being. But there is no error, the mind is more prone to, than, to substitute local, for general ideas; and to limit the boundaries of infi­nite being, to its own finite comprehension. Whereas, it does appear most reasonable, if we apply our mind to a right contemplation of things, and avail ourselves of the analogy of experience and fact, that nature travels on in infinitum. and is equally boundless in magnitude, and prolific in variety.

A late important discovery was made by the celebrated Dr. Bradley, astronomer royal, of the aberration of the fixed stars; this was accidentally made, while endeavouring to ascertain the parallax of be earth’s orbit. This is a variation of their situation, in relation to the plane of the earth’s axis. Mr. Molyneuz and Dr. Bradley began to observe the bright star in the head of Draco, as it passed near the zenith, with an instrument made by Mr. Graham, for the purpose of discovering the parallax, and by often repeated observations, they found the star, about the beginning of March 1726, to be 20 seconds more southerly thin at the time of the first observation. It now indeed seemed to have arrived at its utmost limit southward ; because in seve­ral trials made about this time, no sensible difference was observed in its situation. : by the middle of April it appeared to he returning back again towards the north ; and about the beginning of June, it passed about the same distance from the zenith, as it had done in December, when it was first observed. In September following it appeared 39” more northerly than it was in March, just the contrary way to which it ought to appear by the annual parallax of the stars. This unexpected phenomenon perplexed the observers very much, and Mr. Molyneux died before the true cause of it was discovered. After this Dr. Bradley. with another instrument, more exact, and accurately adapted to the purpose, observed the appearances, not only in that, but many other stars ; and by the great regularity that appeared in a series of obser­vations, made in ;J1 parts of the year. the doctor was full) satisfied with regard to the general laws of the phenomenon, and therefore endeavoured to find out the cause of them. He was already convinced that the apparent motion of the stars, was not owing to a mutation of the earth’s axis. The next thing that offered itself was an alteration in .the direction of the plumb line, by which the instrument was constantly rectified; but this proved insufficient, as well as a trial by refraction. At last this acute astronomer found, that the phenomena in question proceeded from the progressive motion of light, and the earth’s annual motion in its orbit: for he perceived, that if light was propagated in a given portion of time, the apparent place of a fix d object would not be the same when the eye is at rest, as when it is moving in any other direction, than that of the line passing through the eye and the object; and, that, when the eye is moving in different directions, the apparent place of the object would be different, from the true.

10th. The earth, or planet which we inhabit, is the third in magni­tude and distance from the sun. it is computed to he 95.173,000 miles distant from the centre of its attraction, or the body of the sun; round which it revolves in the space of 365 days 5 hours and 49 minutes, or from any equinox, or solstice to the same again, but from any fixed star to the same again as seen from the sun, in 365 days 5 hours 9 minutes ; the former being the length of the tropical year, and the latter the length of the siderial. It travels at the rate of 68,000 miles every hour; a motion, which though upwards of 140 times swifter than a cannon ball, is little more than half as swift as Mercury’s motion in his orbit. The diameter of the earth is 7970 miles; and by turning round on its axis every 24 hours from west to east it causes an apparent motion of all the heavenly bodies from east to west. By this rapid motion of the earth on its axis, the inhabitants about the ‘equator are carried 1042 miles every hour, while those on the parallel of London are carried only about 580, besides the 68 thousand above mentioned, which is common to all places whatever

A variety of circumstances afford the clearest evidence of the globular figure of the earth. 1. When we are at sea, we may be out of sight of land, even when the land i3 near enough to be visible, if it were not hid from the eye by the convexity of the water. 2. The higher the eye, the farther will the view be extended; it is very common for sailors to go up to the top of the mast to look out, as they term it, and thence they will discover land, or ships at a much greater distance than one could do from the deck. 3. When we are on shore, the highest part of a ship is visible at the greatest distance. If a ship is going from us, out to sea, we shall continue to see the mast, after the hull or body has disappeared, and the top of the mast will continue to he seen the longest. If a ship is coming towards us, the top of the mast comes first in view, and we see more and more, till at last the hull appears 4. Several navigators, as Ferdinand Magellan, Sir Francis Drake, Lord Anson, Captain Cook, &c. have sailed round the globe; not in an exact circle, the land preventing them, but by going in and out as the shores happen to lie. 5. All the appearances of the hea­vens are the same, whether at land or sea. 6. Eclipses of the moon arise from the shadow of the earth, which is always circular, although the earth presents, during several hours, different portions of its sur­face to the moon, yet still the shadow is round. The small inequalities upon the surface of the earth, bear no kind of proportion to its magnitude, sufficient to alter the appearance of its shadow. 7. The globular figure of the earth is also inferred from the operation of level ling in which it is found necessary, to make an allowance for the differ­ence between the apparent, and true level.

The earth’s axis makes an angle of 23 1/2 with the axis of its orbit, and its position at any one time, is parallel to its position at any other time. Thus it points always to the same quarter of the heavens throughout its annual course. That the earth moves round the sun, may be proved beyond a doubt, by the following arguments.

1st. The sun is found by the most accurate observations, to be im­mensely larger than the earth; for his diameter, as seen by us, subtends an angle of more than 80’, but it is certain, that the earth were it seen from the sun, would not subtend a greater angle than 1 7”, if, therefore, the sun be formed of materials, not very much rarer than the earth, (and there is no reason to believe it is less dense,) the quantity of matter in the sun, must far exceed the whole mass of matter in all the planets; and to suppose that gravity retains all the other planets in their orbits, with­out affecting the earth, would be as absurd, as to suppose that six cannon bullets might be projected up to different heights in the air, and that five of them should fall to the ground, and that the sixth, though neither the highest nor the lowest, should remain suspended in the air, without falling, and the earth move round it.

There is no such thing in nature as a heavy body moving round a light one, as its centre of motion. A pebble fastened to a millstone by a string, may, by an easy impulse be made to circulate round the mill­stone: but no impulse could make a millstone circulate round a loose pebble; for the millstone would fly off and carry the pebble along with it. The sun is so much bigger and heavier than the earth, that, if he were moved out of his place, not only the earth, but all the planets, even if they were united in one mass, would be carried along with him, as the pebble would be with the millstone.

2. The celestial motions, on this principle become more simple and free of looped contortions, which must be supposed to occur in the other case; and which are extremely improbable, and incompatible with all that we know of motion. 3. If the earth revolve round the sun, then the analogy between the squares of the periodic times, and the cubes of the distances, will obtain in all the bodies, which circulate round a com­mon centre ; whereas this will not be the case with the sun and moon, if both turn round the earth. Besides these, other proofs night be given: but the most complete proof of all, and which indeed amounts to a demonstration is, the aberration of the fixed stars, arising from the progressive motion of light, combined with the earth’s progressive motion round the sun, a discovery made by Dr. Bradley, and one of the finest in modern astronomy.

The strongest objection, that can be urged against the earth’s moving round the sun like the other planets, is that in opposite points of the earth’s orbit, its axis, which always keeps a parallel direction, would point to different fixed stars; which is not found to be fact. But this objection is easily removed, by considering the immense distance of the stars, in respect to the diameter of the earth’s orbit; the latter being no more than a point, when compared to the former. If we lay a ruler on the side of a table, and along the edge of the ruler, view the top of a spire at ten miles distance; then lay the ruler on the opposite side of the table, in a parallel situation to what it had before, and the spire will still appear along the edge of the ruler; because, our eyes even when assisted by the best instruments, are inca­pable of distinguishing so small a change at so great a distance. As the apparent places of the stars, therefore, correspond with this theory, the motion of the earth, and the motion of light are at once determined.

For by frequent observations of the eclipses of Jupiter’s satellites, it is found, that light is about 8 minutes in moving from the sun to the earth. And since the earth describes about I degree, or 3800’ in a day, or 1440 miles in minutes, it will describe 20” in its orbit; there­fore, the velocity of light, is to the velocity of the earth in its orbit, as radius to an arch of 20”, or the third part ofa minute, that is, as one to 0002929/3 or, .00009697, or as 10,300 to 1, that is, the velocity of light is I 0,300 times greater than the velocity of the earth in its orbit.

It is found that the sun, and those planets which have visible spots turn round on their own axes: for the spots in general move regular over their disks, allowing for the variations already noticed. Hence %ve may reasonably conclude, that the other planets on which we see no spots, and the earth which is likewise a planet, have such rotations. ‘But being incapable of leaving the earth to view it at a distance, and its rotation being smooth and uniform, we can neither see it move on its axis as we do the planets, nor feel ourselves affected by its motion.

Yet there is one effect of such motion, which will enable us to judge with certainty, whether the earth revolves On its axis or not.

All globes which do not turn round their axis, will be perfect spheres, on account of the equable pressure on their surface ; especially of the fluid parts. But all globes, which turn on their axis, will be oblate spheroides; that is their surface will be higher, or farther from the centre in the equatorial than in the polar regions: for as the equa­torial parts move quickest, they will recede farthest from the axis of mo­tion and enlarge the equatorial diameter. That our earth is really of this figure, is demonstrable from the unequal vibrations of a pendulum, and the unequal length of degrees in different latitudes -Since then, the earth is higher at the equator than at the poles, the sea, which naturally runs downwards, or towards the places which are nearest the centre, would run towards the polar regions, and leave the equatorial parts dry, if the centrifugal tbrce of those parts, by which the waters were carried there, did not keep them from returning. The earth’s equa­torial diameter, is 36 miles longer than its axis.

It is found that bodies near the Poles are heavier than those towards the equator, because they are nearer the earth’s centre, where the whole force of the earth’s attraction is accumulated. They are also heavier, because their contrifugal force is less, on account of their diurnal motion being slower. For both these reasons, bodies carried from the poles towards the equator, gradually loose their weight. Experiments prove, that a pendulum which vibrates seconds near the poles, vibrates slower near the equator, which shows that it is lighter, or less attracted there. To make it oscillate in the same time, it is found necessary to diminish its length. By comparing the different length of pendulums, swinging seconds at the equator and at London, it is found, that a pendulum must be 2 169/1000 lines (or 12th part of an inch) shorter at the equator than at the poles.

A person on the earth can no more be sensible of its undisturbed motion on its axis, than one in the cabin of a ship, on smooth water, can be sensible of the ship’s motion, when it turns gently and uni­formly round. It is therefore no argument against the earth’s diurnal motion, that we do not feel it; nor are the apparent revolutions of the celestial bodies every day, a proof of the reality of these motions; for whether we, or they revolve, the appearance is the very same. A person looking through the cabin window of a ship, as strongly fancies the objects on land to go round, when the ship turns, as if they were actually in motion.

The other common objections against the earth’s motion on its axis, are easily answered. Some imagine, that if the earth turns eastward, as it actually does, if it turns at all, that a ball fired perpendicularly up in the air, should fall considerably westward of the place it was projected from. This objection will be found to have no weight, if we consider that the gun, and ball, both partake of the earth’s motion: and therefore, the ball being carried forward with the air, as quick as the earth and the air turn, must fall down on the same place. A stone let fall from the top of a main-mast, if it meets with no obstacle, the deck as near the foot of the mast, when the ship sails smoothly along, as when it stands still.

for those scriptural expressions which seem to contradict the earth’s motion, this general answer may be made to them all, that, the scriptures were never intended to instruct us in philosophy, or astro­nomy; and therefore, on those subjects, expressions are not always to be taken in the literal sense, but for. the most part, as accommodated to the common apprehension of mankind. Men of sense, in all ages, when not treating of the science purposely, have used common lan­guage, and it would be absurd to adopt any other, in addressing the majority of mankind. The annual motion of the earth has been effectually confirmed by an argument drawn from the progressive motion of light; and from the same consideration, the truth of the diurnal motion may be completely established.

In consequence of the progressive motion of light, the apparent place of a fixed star is east of its true place, and the difference is pro­portional to the cosine of the stars declination; this displacement of the fixed stars has changed, because of the procession of the equi­noctial points. Therefore, if the diurnal revolution of the heavens were a real motion, the whole heavens must have changed their appearance; and the respective positions of the stars must be very different now, from what they were in the time of Hipparchus. A star which is now near the vernal equinox, must have changed its appa­rent distance at least 50 from another elliptical star which is 60 degrees east of it. Nay it is highly probable, that no zodiacal star could be ever visible; such would have been the direction, that the rays of light must have taken, because of their own proper motion being corn-pounded with that of the star, whose velocity must have been exceed­ingly great,, by reason of its distance from the poles of the motion. But since no such remarkable displacement of the stars has been observed, we may conclude, that the cause which would have pro­duced it, has no existence; and that the revolutions of the heavens is not a real, but only an apparent motion.

From the preceding select remarks and observations, we derive the following satisfactory conclusions. That the earth is a planet, moving in concert with the other planets, and like them, yielding, and exhi­biting all the planetary evolutions, waxing, and waning, and revolving round its primary. That it participates in mutual relations, which are common to the system, of which it is a member. That whatever enters into the composition of the earth, is reciprocated through the system, supplied, and communicated by the current flow of attraction, from globe to globe. That this attraction, is a mutual relation. and Communication between worlds, but that it is diversified in degrees, of strength, as they are diversified in degrees of distance. Hence also we derive the physical conclusion, that two worlds cannot be suspended, and concentrated in the same orbit, or limit of attraction, but that their distances will be in an exact ratio, to the space which they are to occupy: so, that, if two worlds c could coalesce and drop. into one, for instance, the earth and .Jupiter, their new orbit would assume a mean distance, between their separate orbits, somewhere, about the orbit of Mars, and this would occur in consequence of, and in proportion to, the combined attraction of the Two spheres. Could such a phenomenon take place, the new world would immediately assume an orbit, whose distance from its centre would be in proportion to its relative quantity of attraction, to that centre: arid the new world would immediately assume, also, a rotatory motion on its axis, which would be in an exact ratio, to the proportion of its equatorial diameter, and its distance from the centre of revolving motion. Finally, we learn from this general review, that the same extensive and universal relations prevail, through the continuity of divisions, and subdivisions of worlds, and systems of worlds, as if the materials of the universe were spread out in uniform consistence, and rendered independent of the mundane laws of density, and rarefaction; gravi­tation, and attraction; concretion, and expansion; the general laws of motion and revolution; so that no arguments can weigh against the infinite continuity of worlds, and systems of worlds.

The different seasons which we experience, are owing to the obli­quity of the axis of rotation of the earth, to the plane of the earth’s orbit. But if the axis were perpendicular to it, there could be no variety in the length of days, in whatever part of the orbit the earth was; and all seasons would be alike. Thus the obliquity of the earth’s axis, to the ecliptic, or which is the same thing of the equi­noctial to the ecliptic, is the cause of the different seasons, summer, winter, spring and autumn, during the year. Without this, there could be no difference of seasons; and consequently it could not be easy to know the length of the year, without observations of the stars. For the length of the year is known from the time of observation, when the sun is in the equinoctial points ; and there being no such points to observe by, there could be no method but to observe by the position of the stars, when the same star was again in opposition to the sun, which none but an astronomer could do.

The sun appears 47 degrees higher in the summer tropic, than it does in the winter tropic; this phenomenon may be thus represented: take a small globe that has the equinoctials and parallels drawn upon it; and placing a candle upon a table, move the globe round the candle in a circle parallel to the table, so that the axis of the equator may be oblique to that circle, and be kept always in a parallel position whilst it moves about. The candle will illuminate the globe as it is carried round, just as the sun does the earth in its orbit; and the parallels will be the same way affected with light and darkness the globe.

The opinion of astronomers, that the orbit of the earth being and the sun constantly keeping in its lower focus, which according to calculation, is, 1,617,941 miles from the middle point of the larger axis, the earth approaches twice as near, or, by computation 3,235;882 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 in our summer, proves that our earth approaches nearer the sun in winter, than in summer. ‘But here a very serious difficulty occurs, which they appear not to have been aware of, they did not consider in this instance, that whilst it was winter in the northern regions, it was summer in the southern regions of the earth, and that it was im­possible, that the earth in 400 of north latitude, could be 3,235,832 miles nearer the sun, than the same earth in 400 of south latitude, the direct difference of which situations, would only amount to a very few miles, in proportion to the angular obliquity of the opposite points of parallel latitudes, north and south; they did not consider, that the part of the earth, which is nearest the sun, is that point on its cir­cumference which has the sun in its zenith at meridian, and that in twelve hours time, that point of its circumference would be farthest from the sun: the angular phenomenon, on which astronomers have founded the hypothesis, vanishes at the equator, and in opposite parallels of latitude, consequently the hypothesis itself falls to the ground.

No part of the earth, can, at the same time, be farther from the sun than another, at a distance exceeding its diameter, or 7964 miles, and that point of the earth which is nearest the sun at meridian, is farthest from it at midnight. One astronomer in 40° of north latitude computes the earth to be 3 1/4 millions of miles nearer the sun, in his northern winter, than it was in his northern summer; while an astronomer, in 40° of south latitude, at the very same instant, and from the very same data, is calculating the same earth to be 3 1/2 millions of miles, farther from the sun than the northern astronomer. while the diameter of the earth itself does not extend to 8000 miles. These remarks are only intended to apply to the hypothesis, that the earth is nearer the sun in winter than in summer, they are not intended to affect, by any means the doctrine of the ellipsis of the earth’s orbit, or to deny its perihelion and aphelion distances. Nor is it intended to deny that the earth is in its perihelion in winter; but it should be recollected, that if the earth is in its perihelion in winter, it is also in its perihelion in summer; for there is no winter but there, is at the same time a summer, and it is evident, that the part where it is summer, is nearer the sun, than the part where it is winter, and this for the reasons before assigned, viz, that of the direct position, of a point of the earth’s circumference to the sun: for the position of all the parts of the earth, where it is summer, is more direct, than the parallel parts where it is winter. Besides, from the nature of an ellipsis, the earth in its complete revolution, must be twice in is aphelion, and twice in its perihelion: and the difference of time will be, half, or the earth will be alternately in its perihelion, and aphelion every six months: consequently, if the earth is in its perihelion in winter, it will also be in its perihelion in summer, for the distance of time is six months, the distance mentioned. And the northern parts of the earth, cannot be in aphelia, at the same time that the southern are in perihelia Therefore, when it is winter in the north, and summer in the south; or summer in the north, and winter in the south, then is the earth in perihelia, then, computing the distance, the earth is 3,235,882 miles nearer the sun, than, when it is in the vernal and autumnal equinoxes: at which seasons, the atmosphere of the earth is more dilated and enlarged, than at the solstices, in consequence of the direct force of attraction, operating on the centre of its disk.

The MOON is not a primary planet, but only a satellite, Or attendant on the earth, circulating round it in 29 days, 12 hours, 44 minutes, and round the sun along with the earth in a year. The moon’s dia. meter is computed at 2180 miles; and her distance from the earth's centre 240,000; the period of her revolution in her orbit is 27 days, 7 hours, 43 minutes, moving at the mean rate of 2290 miles an hour; she is stated to revolve on her axis, in exactly the same time that she moves round the earth, which is the occasion of her exhibiting always the same face to us, and consequently her day and night taken together is as long as our month.

The moon, like the earth, is an opaque globe, and shines 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 disappears when she comes between us and the sun; because then her dark side is turned towards us. When she is gone a little way forward, we see a little of her enlightened side, which increases to our view as she advances until she comes opposite to the sun; when her whole enlightened side is towards us, and she appears a round illuminated orb, which we call the FULL MOON; her dark side being then turned away from the earth. From the full she seems to decrease gradually, as she goes through the other half of her course, showing us less of her enlightened side every day, till her next change or conjunction with the sun, when she disappears as before.

The earth being an opaque body must appear as a moon, to the inhabitants of the moon, waxing and waning regularly, but appearing 13 times as big, and affording them 13 times as much light as she does 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 vice versa. From these peculiar circumstances of the month, the earth is never seen at all from the side opposite to the earth; from the middle of the other half it is always seen over bead; turning round almost 30 times as quick as the moon does. From the circle which our view of the moon, only one half of the earth’s side next her is seen; the other half being hid below the horizon of all places On that circle. To her inhabitants the earth appears the biggest body the universe, appearing full 13 times as big as she does to us.

It has been observed by astronomers that the axis of the moon, is so nearly perpendicular to the ecliptic, that the sun never removes sensibly from the equator; and the obliquity of her orbit, as seen from the sun, which is next to nothing, cannot cause any sensible declination. Yet her inhabitants are not destitute of means for ascer­taining the length of their year, or period of her revolution round the sun: though their method must be different from ours. We know the length of our year by the return of our equinox; but the Lunarians having always equal day and night, must have recourse to another method arid we may suppose, they measure their year by observing when either of the poles of our earth begins to be enlightened, and the other to disappear, which always takes place at our equinoxes: being conveniently situated to observe any particular phenomenon attached to our globe, and which must be extremely conspicuous to them. The year is of the same absolute length to the inhabitants of the earth and moon though very different as to the number of days; we having 365,k days, and the Lunarians only 1 27/19 every day and night in the moon, being as long as 29 1/2 on the earth.

The inhabitants of the moon on the side next the earth, may find the longitude of their places, as easily as we can find the latitude of ours: for the earth being constantly or very nearly so, over one meridian of the moon, the east and west distances of places from that meri­dian are as easily found, as we can find our distances from the equator, by the altitude of our celestial poles.

As the sun only enlightens that half of the earth which is towards it, and leaves the opposite half in darkness, so he does the same to the moon, but with this difference, that as the earth is surrounded with a superior atmosphere, we have twilight after the sun sets, and before he rises; but the moon, (as is supposed,) having no atmosphere of her own, must have an immediate transition from the brightest sunshine to the blackest darkness.

The moon being an opaque spherical body, we can only see to part of her enlightened half, which is towards the earth. And the fore, when the moon is between us and the sun, her dark side is turn towards the earth, and she totally disappears, there being not light enough on that half to render it visible. When she comes to first octant, or has gone an eighth part of her orbit, from her conjunction, a quarter of her enlightened side is towards the earth, and appears horned. When she has gone a quarter of her orbit, in between the earth and the sun, she shows us one half of her enlightened side, and we say she is a quarter old. When she gains he third o