“In larger circuit rolls the orb of Mars,Guiltless of stern debate, and wasteful wars,As some have erring taught: he journies on,Impell’d and nourish’d by the attractive sun;Like us, his seasons and his days he owesTo the vast bounty which from Phœbus flows.”
“In larger circuit rolls the orb of Mars,
Guiltless of stern debate, and wasteful wars,
As some have erring taught: he journies on,
Impell’d and nourish’d by the attractive sun;
Like us, his seasons and his days he owes
To the vast bounty which from Phœbus flows.”
His figure, like that of the earth, is an oblate spheroid. His mean distance from the sun is 145,000,000 miles, and he travels round that common centre of gravity in about 687 of our days, or 1 year, 321 days, 22 hours, 18 minutes, 27 seconds, which is nearly equal to two of our years; and therefore his velocity in his orbit is at the rate of 55,000 miles an hour. He has likewise a rotation upon his axis, which is performed in 1 day, 39 minutes, 22 seconds. This was discovered by means of spots seen on his surface. Dr. Hook, in 1665, observed several spots, which, having a motion, he concluded that the planet revolved upon its axis. In 1666, M. Cassini saw several spots in the two hemispheres of Mars, which, by continuing his observations very diligently, he found to move from east to west, and to return in the space of 24 hours, 40 minutes, to their former situation. Whence both the motion and period, ornatural day of this planet, were determined. In 1781, Dr. Herschell observed the spots of Mars very minutely, from the motion of which he has found his rotation upon his axis to be performed in 24 hours, 39 minutes, 21-2/3 seconds; and he says that there cannot be more than two seconds of uncertainty in this result. The different seasons will take place on this planet very much like what they are known to do upon our earth, with this difference, that the seasons there will be almost as long again as with us, on account of the time he takes in moving round the sun being nearly twice as long as our year. The diameter of Mars being 4,135 miles, he is about 2/11, or less than a fifth, and more than a sixth part as large as the earth; and if any moon attend him, she must be very small, for it has not yet been discovered by the best telescopes of our most eminent astronomers; if without a moon, walking his round in perpetual solitude, he must consequently want that division of time, which, from the moon’s revolution round the earth, is called a month.
From the greater distance of Mars in his orbit than our earth is, the inhabitants there will scarcely see Mercury, unless it be when he appears on the sun’s face, and passes over him like a dark spot, in the same manner as he sometimes does to us. Venus will to them appear somewhat similar to the appearances of Mercury to our earth, the apparent distance from the sun being nearly the same to them as Mercury is to us. Our earth to them, also, will be an inferior planet, or within his orbit, being nearer to the sun, in a way similar to what Venus appears to us, and will alternately be a morning or evening star; and our moon, which will always be seen to accompany her, when in a position to have the benefit of the sun’s light, will not be seen at a greater distance, than about a semi-diameter of the sun or moon from it.
This planet being half as far again from the sun as our earth is, his light and heat are not half so much as our own. When in opposition to the sun, he is found to be five times nearer to us than when in conjunction; and, therefore, he appears so much bigger and brighter at one time than another. In 1719, his apparent magnitude and brightness were so much increased, that, by the uninformed, he was taken for a new star.
The telescopic appearance of Mars is very variable. This planet exhibits larger and more remarkable spots than any of the others. The belts and cloudy appearances are found to change their shape and arrangement frequently. The predominant brightness of the polar regions leads to the supposition that those parts of his surface, like the poles of the earth, are intensely frozen, or always covered with snow; and Dr. Herschell imagines that the changes in brightness are connected with the summer and winter seasons on that planet. The phases of Mars were first discovered by Galileo. Having his light from the sun, and revolving round it, he has anincrease and decrease like the moon. At his quadratures, he appears gibbous, but never horned, like Venus, Mercury, and the Moon; which shows, that his orbit includes that of the earth, and that it is from the sun that he receives his light.
Between the orbit of Mars and that of Jupiter, the smaller planetary bodies, lately discovered, revolve.Cereswas discovered on the 1st of January, 1801, by M. Piazzi, astronomer at Palermo, in the island of Sicily. When viewed through a good telescope, it is of a ruddy color, appears to be of the size of a star of the eighth magnitude, and surrounded with a dense atmosphere. Her mean distance from the sun is 260,000,000 miles; and her revolution is performed in 4 years, 7 months, 10 days. Dr. Herschell and Schroëter differ very much as to the magnitude of this planet; the former says the diameter is only 160 miles, but the latter makes it more than ten times greater, or 1,624 miles.Pallaswas discovered on the 28th of March, 1802, by Dr. Olbers, of Bremen. Its mean distance from the sun 270,000,000 miles; its diameter 80 miles; and it performs its revolution in about 4 years, 280 days.Junowas discovered on the 1st of September, 1804, by M. Harding, of Lilienthal. Its mean distance from the sun is 290,000,000 miles; and its diameter is 119 miles, and the time of revolution round the sun 5 years, 181 days.Vestawas discovered by Dr. Olbers, on the 29th of March, 1807. It is nearer to Mars than either of the other newly discovered planets; and the revolution through its orbit is performed in less time. The size of this planet is not known. Its light is more intense, pure, and white, than any of the other three.
A century and half ago it was conjectured, says a very intelligent author, that there must be a planet between the orbits of Jupiter and Mars, on account of the distance subsisting between those two planets. The discovery of Ceres confirmed this happy conjecture; but the opinion which it seemed to establish respecting the harmony of the solar system, appeared to be completely overturned by the discovery of Pallas and Juno. Dr. Olbers, willing to find a theory that should account for the facts newly ascertained, imagined that these small celestial bodies were merely the fragments of a larger planet, which had burst asunder by some internal convulsion, and that several more might yet be discovered between the orbits of Mars and Jupiter. He therefore concluded, that though the orbits of all these fragments might be differently inclined to the ecliptic, yet, as they must have all diverged from the same point, they ought to have two common points of re-union, or two nodes in opposite regions of the heavens, through which all the planetary fragments must sooner or later pass. One of these nodes Dr. Olbers found to be in Virgo, and the other in the Whale; and it was actually in the latter of these regions that M. Harding discovered the planet Juno. With the intention, therefore, ofdetecting other fragments of the supposed planet, Dr. Olbers examined, thrice every year, all the little stars in the opposite constellation of the Virgin and the Whale, till his labors were crowned with success, by the discovery of a new planet in the constellation of Virgo, to which he gave the name of Vesta.
The existence of four planets between the orbits of Mars and Jupiter, (continues the same author,) revolving round the sun at nearly the same distances, and differing from all the other planets in their diminutive size, and in the form and position of their orbits, is acknowledged to be one of the most singular phenomena in the history of astronomy. The discordance of these phenomena with the regularity of the planetary distances, and with the general harmony of the system, naturally suggests the opinion, that the inequalities in this part of the system were produced by some great convulsion, and that the four planets, as we have already hinted, are the fragments of a large celestial body, which once existed between Mars and Jupiter. To suppose them independent planets, as they must necessarily be if they did not originally form one, their diminutive size, the great eccentricity and inclination of their orbits, and their numerous intersections, when projected on the plane of the ecliptic, are phenomena absolutely inexplicable on every principle of science, and subversive of that harmony and order which before the discovery of these bodies, seemed to pervade the planetary system. Admitting, however, the hypothesis that these planetary bodies, are the remains of a larger body, which circulated round the sun, nearly in the orbit of the greatest fragment, the system resumes its order, and we discover a regular procession in the distances of the planets, and a general harmony in the form and position of their orbits. But, independently of analogical reasoning, the elements of the new planets furnish several direct arguments, drawn from the eccentricity and inclination of their orbits, and from the position of their perihelia and nodes; and all concurring to show, that the four new planets have diverged from one point, and have, therefore, been originally combined in a larger body.
Jupiteris the largest of all the planetary bodies, and, next to Venus the brightest. He was called by the GreeksΖευς, which is fromζεω,to be hot, or, says Parkhurst, immediately from the Hebrewזיto shine, compounded, perhaps, withישsubstance, q.d.the shining substance; a name very justly given to this planet, on account of his strong and clear light.
——“In distant skiesRevolves the mighty magnitude of Jove,With kingly state, the rival of the sun.”
——“In distant skies
Revolves the mighty magnitude of Jove,
With kingly state, the rival of the sun.”
His mean distance from the sun is 490,000,000 miles, and his diameter is 89,170 miles, or more than 11 times that of the earth, and therefore his magnitude is 1,400 times greater than our earth;of course, as the surface of a globe increases according to the square of its diameter, our earth will, to the inhabitants of Jupiter, appear 121 times less than this noble planet appears to us. His revolution round the sun, from east to west, is performed in 11 years, 315 days, 14 hours, 39 minutes, 2 seconds, which is nearly twelve of our years; and his motion in his orbit is 29,000 miles an hour. He performs his diurnal rotation upon his axis in 9 hours, 55 minutes, 33 seconds, by which motion his equatorial parts are carried round at the amazing rate of 26,000 miles an hour, which is about twenty-five times the velocity of the like parts of our earth. He has, of course, a rapid succession of days, as the poet observes,
“In ample compass Jove conducts his sphere,And later finishes his tedious year;Yet swiftly on his axle turn’d, regainsThe frequent aid of day to warm his plains.”
“In ample compass Jove conducts his sphere,
And later finishes his tedious year;
Yet swiftly on his axle turn’d, regains
The frequent aid of day to warm his plains.”
The axis of Jupiter is nearly perpendicular to his orbit, so that he has no sensible change of seasons. This is not the work of chance, as Dr. O. Gregory observes, but wisely ordered by the Divine Architect; for if the axis of this planet were inclined any considerable number of degrees, so many degrees round each pole would be almost six years together in darkness. And as each degree of a great circle on this planet contains more than 700 miles, it is natural to conceive, that vast tracts of land would be rendered uninhabitable by any considerable inclination of his axis.
The appearance of this planet, through a telescope, opens a vast field for interesting inquiry. His surface is not equally bright, but variegated with certain bands, or belts, of a dusky appearance: they run parallel to each other, and are continued round the body of the planet. They are not regular or constant in their appearance: sometimes only one is seen; at other times six or eight. The breadth of them is likewise variable; one belt is sometimes becoming narrow, while another, in its neighborhood, grows broader as if one had flowed into the other: in these cases, an oblique belt has been observed to be between them, as if for the purpose of establishing a communication. Sometimes, one or more spots are formed between the belts, which increase till the whole is united in a large dusky belt. There are also bright spots to be discovered on Jupiter’s surface; these are rather more permanent than the belts, and re-appear after unequal intervals of time. The remarkable spot, by whose motion the rotation of Jupiter upon his own axis was first ascertained, disappeared in the year 1694, and was not seen again till 1708, when it re-appeared exactly in the same place, and has been occasionally seen ever since.
Jupiter is enlightened by four moons, or satellites, each of them larger than that with which we are supplied, and which revolve at different distances from that planet. In the solar system the moons, or satellites, revolve round their respective primary planets ascentres, in the same manner as the primary planets revolve round the sun. By means of Jupiter’s satellites, a method has been obtained for demonstrating that the motion of light is progressive, and not instantaneous, as was formerly supposed; which discovery is important to the interests of science. M. Huygens, in his Treatise on Light, concludes from these eclipses, that light transmits itself about 600,000 times faster than sound.
They are thus referred to by Mallet:
“About him roundfourplanetary moons,On earth with wonder all night long beheld,Moon above moon, his fair attendants dance.”
“About him roundfourplanetary moons,
On earth with wonder all night long beheld,
Moon above moon, his fair attendants dance.”
To a spectator placed on the surface of Jupiter, each of the satellites would put on the phases of the moon; but as the distance of any of them from Jupiter is but small, when compared with the distance of that planet from the sun, the satellites are therefore illuminated by the sun very nearly in the same manner with the primary itself; hence they appear to us always round, having constantly the greatest part of their enlightened half turned towards the earth: and indeed they are so small, that were they to put on the phases of the moon, these phases could scarcely be discerned through the best telescopes. When the satellites pass through their inferior semicircles, they may cast a shadow upon their primary, and thus cause an eclipse of the sun to his inhabitants; and in some situations this shadow may be observed going before or following the satellite. On the other hand, in passing through their superior semicircles, the satellites may be eclipsed in the same manner as our moon by passing through the shadow of Jupiter: and this is actually the case with the first, second, and third; but the fourth, by reason of the extent of its orbit, passes sometimes above or below the shadow, as is the case with our moon.
These satellites were first discovered on the 7th of January, 1610, by the celebrated Galileo, who called themMedician Stars, in honor of the family of the Medici, dukes of Tuscany, his patrons. These satellites, revolving about Jupiter at different distances, from west to east, when viewed through a telescope, make a beautiful appearance. As our moon revolves round the earth, enlightening the nights, by reflecting the light she receives from the sun; so these satellites, revolving round Jupiter, may also be supposed to enlighten the nights of that planet.
Saturnis a very conspicuous planet, though he shines with a pale and feeble light, very unlike that of Jupiter and the otherplanets. He was called by the Greeksφαινων. “From the account given by Diodorus Siculus,” says Costard, “it seems as if the Chaldeans called this planet by some name not widely different from this of the Greeks. In the language of Chaldea, the verbפנאphana, orפנהphanah, signifiesconvertere se,divertere se,declinare. And whatevervanishes, ordisappears, very properlydeclines, orturns aside, from our view. This planet, therefore, was most probably calledפן_phen_, orפיןphain, and, with a Greek termination,φαινων, on account of hiswithdrawinghimself, by reason of his distance. And this conjecture is yet further confirmed from his name in another dialect, or among another people. For fromסתרsater, latuit, abscondit se, with the paragogicןnunwhich is not unusual in the formation of Eastern words, comes the wordסתרןSaturn, and with the Latin terminationus, Saturnus.”
His mean distance from the sun is 900,000,000 miles, consequently his motion in his orbit is proportionably slow; and his annual revolution round the sun, from west to east, being so much longer likewise than that of the other planets, he takes 29 years, 164 days, 7 hours, 21 minutes, 50 seconds, which is almostthirtyof our years, to accomplish it, in his orbit travelling with a velocity of 22,000 miles an hour. His diameter is 79,000 miles; and his magnitude is about 1,000 times that of the earth. The time of rotation upon his axis is 10 hours, 17 minutes.
“Still further off, scarce warm’d by Phœbus’ ray,Through his wide orbit, Saturn wheels away;How great the change, could we be wafted there!How slow the seasons! and how long the year!”
“Still further off, scarce warm’d by Phœbus’ ray,
Through his wide orbit, Saturn wheels away;
How great the change, could we be wafted there!
How slow the seasons! and how long the year!”
There is a singular and curious appendage to Saturn, namely, a thin, broad, opake ring, encompassing the body of the planet, without touching it; like the horizon of an artificial globe; it appears to be suspended round the planet, and to keep its place without any immediate connection with it. The distance of this prodigious circle from the body of the planet is usually stated to be about 21,000 miles.
The dimensions of the ring, or of the two rings with the space between them, Dr. Herschell has given as follows:
It puts on different appearances to us, sometimes being seen quite open, or as a wide oval, and at others, only as a single line. When our eye is in the plane of the ring, or looking at it directly on theedge, it is invisible to us; and it is in this situation twice in each revolution of the planet; that is, once in about fifteen years: at these times, he appears quite round, for nine or ten months together. The ring was invisible to us on the 15th of June, 1803, and, since that time, gradually increased in light and breadth for about seven years: and, after which, has again decreased, till, as before, after an interval of fifteen years, in the present year 1818, the ring is again edgewise to us, and invisible. With telescopes of great magnifying power, two belts or stripes have been discovered on Saturn; they appear parallel to the ring, and are supposed to be permanent. Of what component materials this ring is composed, or by what means it is suspended, we as yet remain ignorant: but of its use, it is supposed to supply light and heat to the planet, agreeably to the observation of a poet who has evinced an extensive acquaintance with philosophy.
“Muse! raise thy voice, mysterious truth to sing,How o’er the copious orb a lucid ring,Opake and broad, is seen its arch to spread,Round the big globe at stated periods led;Perhaps (its use unknown) with gather’d heatTo aid the regions of that gelid seat,The want of nearer Phœbus to supply,And warm with reflex beams his summer sky;Else might the high-plac’d world, expos’d to frost,Lie waste, in one eternal winter lost.”
“Muse! raise thy voice, mysterious truth to sing,
How o’er the copious orb a lucid ring,
Opake and broad, is seen its arch to spread,
Round the big globe at stated periods led;
Perhaps (its use unknown) with gather’d heat
To aid the regions of that gelid seat,
The want of nearer Phœbus to supply,
And warm with reflex beams his summer sky;
Else might the high-plac’d world, expos’d to frost,
Lie waste, in one eternal winter lost.”
Besides the ring, Saturn is also furnished with seven attendant moons, or satellites, which move around him at different distances, in a way similar to those of Jupiter.
The sixth and seventh satellites were discovered by Dr. Herschell in 1787 and 1788: they are nearer to Saturn than any of the other five; but, to prevent confusion, they have been called the 6th and 7th. The 5th satellite has been observed by Dr. Herschell to turn once round its axis, exactly in the time in which it revolves round Saturn: in this respect it resembles our moon. Their distance from us is so far, as not to be easily visible, even with a good telescope, unless the air be exceedingly clear.
It was for ages that astronomical science limited the solar system to six planets, and Saturn was considered as its utmost extent. Vitruvius, speaking of the planet Saturn, says, that star “is nearthe extremity of the world, and touches the frozen regions of heaven.” He did not understand the extent of our planetary system.
It is to the indefatigable application of Dr. Herschell that we are indebted for the discovery of a new planet, which is the fourth of the superior ones then known, and, being at twice the distance of Saturn from the sun, has quadrupled the bounds formerly assigned to the solar system. This planet was discovered on the 13th of March, 1781, and is called by different names: the discoverer bestowed upon it that ofGeorgium Sidus, in honor of our present venerable and beloved sovereign; by the French it is calledHerschell, and by the Italians,Uranus. This important discovery is very deservedly noticed by the Poet Laureat, in his Ode entitled “Carmen Seculare for the year 1800.”
“Mathesis with upliftedeye,Tracing the wonders of the sky,Beholds new constellations rise,New systems crown the argent skies;Views with new lustre round the glowing pole,Wide his stupendous orb theGeorgian Planetroll.”
“Mathesis with upliftedeye,
Tracing the wonders of the sky,
Beholds new constellations rise,
New systems crown the argent skies;
Views with new lustre round the glowing pole,
Wide his stupendous orb theGeorgian Planetroll.”
On the 11th January, 1787, Dr. Herschell discovered the second and fourth satellites which attend his own planet the Georgium Sidus; and in the following years, previously to 1791, he observed four others revolving round the same body. Though this celebrated astronomer was the first who discovered the Georgium Sidus to be one of the planets of the solar system, yet no doubt can be entertained of its having been before observed and considered as a fixed star. Flamsteed in 1690, Mayer in 1756, and Monnier in 1769, determined the places of three stars which cannot now be found. And M. La Place, according to his theory of Jupiter and Saturn, has found that the Georgium Sidus wasexactlyin those three points at those very times. These truly singular occurrences leave no doubt of the identity of these three stars with the new planet. The lines which Mallet applied to Saturn are now, with a little alteration, more applicable to the Georgium Sidus, or Herschell planet.
“Last, outmost Herschell walks his frontier round,The boundary of worlds; with his pale moons,Faint-glimmering through the darkness night has thrown,Deep-dy’d and dead, o’er this chill globe forlorn:An endless desert, where extreme of coldEternal sits, as in his native seat,On wintry hills of never-thawing ice;Such Herschell’s earth.”
“Last, outmost Herschell walks his frontier round,
The boundary of worlds; with his pale moons,
Faint-glimmering through the darkness night has thrown,
Deep-dy’d and dead, o’er this chill globe forlorn:
An endless desert, where extreme of cold
Eternal sits, as in his native seat,
On wintry hills of never-thawing ice;
Such Herschell’s earth.”
His mean distance from the sun is about 1,800,000,000 miles, and he performs his revolution from west to east round the sun in 83 years, 294 days, 8 hours, 39 minutes; and in his orbit he moves with a velocity of 15,846 miles an hour. His diameter is 4½ times larger than that of the earth, being more than 35,000 miles; and his magnitude is 80½ times larger than that of the earth. The orbit in which he revolves is nineteen times further from the sunthan the earth’s orbit; consequently he has 361 times less light and heat from the sun than we have. Notwithstanding this, his proportion of light is considerable; for having been calculated, it is found to be equal to the effect of 284 of our full moons. When the sky is very serene and clear, and the moon absent, this planet may be perceived with the naked eye, unassisted by a telescope: and it appears as a star of the fifth magnitude, with a blueish white light, and a brilliancy between that of Venus and the Moon.
The want of light arising from the great distance of this planet from the sun, is supplied by six satellites, which revolve at different distances round their primary.
All these satellites, it has been said, perform their revolutions in their orbits contrary to the order of the signs; that is, their real motion is retrograde, but probably, as suggested by Dr. Hutton, this is an optical illusion.130As the indefatigable Dr. Herschell has already discovered six satellites belonging to this planet, does not its immense distance from the sun leave some ground for conjecture, that there may remain some undiscovered, and that his attendants are as numerous, if not more so, than those of Saturn?
The mark which characterises the planet Herschell is the initial of the discoverer’s name, intersected by a cross bar to represent a cross, by which to denote that the discovery of the planet took place after the birth of Christ.
Astronomy produces calculations concerning the magnitudes, distances, and revolutions of the planets, and their respective satellites,which, to the uninformed, appear absurd, chimerical, and presumptuous; while, probably, they laugh at such notions as were received among men, when even the wisest of them were weak enough to believe, that the earth was an immense plain, situated in the centre of the universe; that the vault of heaven was of crystal; and that the sun was no other than a plate of red hot iron, about as large as the Peloponnessus. The following thoughts, communicated by my much esteemed friend Thomas Exley, A. M. may assist such persons to entertain more favorable sentiments of the science of astronomy, and also serve to enlarge their views of the Supreme Being.
“Many persons who have not had the advantages of proper instruction in mathematical science, cannot be persuaded that it is in the power of man to ascertain the distances of the sun, moon, and planets, and, of course, pay little regard to the assertions of astronomers on this subject. Sometimes, they are bold enough to say the thing is impossible, because no one has ever been to any of those bodies. Let such persons consider, that it is not necessary to go to a remote object in order to measure its distance; for that purpose, it will be sufficient to know the length of a line at the place of the spectator, and the inclination of this line to two others directed from its extremities to the object; for, on the length of this line, and the position of the two others, depends the distance of the object from the ends of that line.
“Thus, if I wish to know the distance of a neighboring tower, or other object beyond a river, or in some other way inaccessible; I measure any convenient line terminating in my station, and by some instrument proper for measuring angles, I ascertain the position of my measured line to the lines connecting its extreme points and the object. On these data depends the distance, and from this line and these angles accurately measured, the exact distance may be with great ease truly found. It is on similar principles that astronomers investigate the distances of the heavenly bodies. They take as the given or measured line, which may be called the base, some line on the earth, the semi-diameter for instance, as being the most convenient. The angle formed, or rather contained by two lines drawn from the sun or planet to the ends of the semi-diameter of the earth, is called the parallax, because it shows the difference of the apparent situation of the object as seen from the extremities of the semi-diameter, that is, it measures the arc of a great circle in the heavens contained between its two apparent places. Hence to ascertain its parallax, or difference of the apparent place when the object is viewed from the other end of the semi-diameter, becomes a problem of great importance in astronomy; for this being truly discovered, the distance of the planet will be obtained with the utmost exactitude. If any other line besides the semi-diameter of the earth, whose length and position areknown, be used as a base, and the parallax in respect of this line be found, the same conclusions will follow. The chief difficulty in this affair arises from the smallness of the angle to be measured, which is a consequence of the greatness of the distance in respect of the earth’s semi-diameter. Several ingenious methods have been proposed and employed by astronomers to discover the distances of the sun and planets, but nothing serves this purpose so well as the transits of Venus over the sun’s disk. At certain periods, which can be foretold by astronomers, this planet passes exactly between us and the sun, and is seen as a dark round spot for some hours, moving in a line across the sun’s face or disk. The observer should be furnished with a good chronometer, or pendulum clock with seconds, to note the time of the transit; and good instruments, to take the apparent diameters of the sun and Venus, and her greatest distance from the sun’s limb while passing over his disk: from these observations, and the known phenomena of the motions of the earth and Venus, the parallax may be found. But if two observers, at very distant places of the earth properly chosen, make these observations, the parallax may be obtained with much greater ease and nicety; because the distance of the apparent tracks of Venus across the sun as seen from the two places, and also the difference of the time of the passage, arises from the parallax of Venus and that of the sun. The two last transits, which happened in the years 1761 and 1769, were carefully observed for this purpose; and it is to the results of these observations that the present astronomers are indebted for their more accurate knowledge of the distances of the planets, and the dimensions of the solar system.
“It should be observed, that if the parallax, and consequently the distance of any one of the planets by any means becomes known, the same is easily obtained for each of the other planets, from the relation which has been clearly discovered to subsist between the periodical times of revolution of the planets round the sun, and their distances from that central luminary. Astronomers have most decidedly proved that the square of the time in which any planet revolves is to the square of the time in which any other revolves, as the cube of the distance of the first, is to the cube of the distance of the other; and since all the times are known from observation, if the distance of any one be determined, there is no difficulty at all to find the distances of all the other planets from the sun.
“It has also been matter of great surprise to the unlearned, that astronomers should pretend to tell the magnitudes of the sun and planets. But this is no difficult problem when the distance is known. Theapparentdiameter is readily found from observation, and on this and the distance depends thetruediameter. If the apparent diameters of two objects be equal, the true diameterof the one will be greater as it is more remote; and the apparent diameter of any object will increase as the distance of it from the observer diminishes. From this every one sees, that a knowledge of the distance of the object is an indispensible element for finding its bulk; and, according to the accuracy of the measure of the distance, will be that of the measure of the magnitude, provided the apparent distance be truly taken; and this, in the present improved state of our instruments, presents no obstacle. There can be no doubt but that astronomers are very near the truth in the numbers which they now give us for expressing the distances and magnitudes of the sun and planets.
“The telescope has been of singular use to the astronomer; it has shown him many phenomena of the heavenly bodies, concerning which he would otherwise have been totally ignorant. It is by the assistance of this noble instrument that we have attained to the knowledge of the rotations of the sun and planets, the phases of Venus and Mercury, Saturn’s ring, and many other particulars exceedingly interesting. The telescope has discovered several planets which otherwise would have revolved in their courses unknown and unnoticed by the inhabitants of this globe; it has informed us that several of the planets have moons moving round them, as our moon revolves round the earth; besides, it has presented to our view an innumerable multitude of fixed stars which without this assistance we should never have seen.
“It is no wonder that great efforts have been made to improve this excellent instrument; these efforts have been attended with great success, and what may be further done in this respect we cannot tell; however, there is a limit to the improvements of the telescope, for after it has attained a certain degree of magnifying power, the motes and vapors in the atmosphere would be so magnified as to occupy its whole field of view, and thus render it a useless incumbrance.”
Who can contemplate the power which produced the solar system, at once so magnificent, beautiful, and delightful, without astonishment and admiration? The planets are kept in a regular motion, and retained in an invariable course round the sun, by the power of this luminary’s attraction or gravity. These bodies have a projectile force, being propelled forwards in a right line, which is the nature of all simple motion; but the sun’s attraction combining with their own projectile force, withdraws them from their rectilineal courses, and preserves the most perfect harmony in the system. This wonderful mechanism was originally impressed on the system by its infinitely wise and omnipotent Creator; to which primary impulse it has with undeviating uniformity adhered, having never suffered in its operations from the greatest distance of space, or intervals of time!
Surely no power less than that which at first gave existence and modification to matter, is equal to the government of the world.The solar orb and the planetary bodies could no more subsist in their present form and order, without a Divine, supporting, and directing hand, than they could at the beginning make themselves. What is that general law or force calledgravitation, without which the whole frame of nature would soon be dissolved? Is it not a power constantly issuing from the Deity, and which if he should suspend but for one moment, the whole creation would sink into ruins? How inconceivably great and operative must that power be, that is present throughout the universe, with all the heavenly orbs to preserve them in their courses; and on this earth, with every creature, and every particle of matter, to preserve its present form!
In addition to the planets and their satellites, there areComets, which revolve round the sun, and, consequently, are a part of the solar system. They have often a long tail, in appearance resembling hair, issuing from that side which is turned away from the sun. Comets are popularly divided into three kinds, namely, bearded, tailed, and hairy: but this arrangement seems to apply rather to the different circumstances of the same comet, than to the phenomena of several. Thus, when a comet is eastward of the sun, and moves with him, it is said to be bearded, because the light precedes it in the manner of a beard: but when it is westward of him, it is said to be tailed, because the train of light follows it in the manner of a tail: and, lastly, when the sun and comet are diametrically opposite, the earth being between them, the train is hid behind the body of the comet, excepting the extremities, which being broader than the body of the comet, appear round it like a border of hair (coma), from which circumstance it is said to be hairy, and is denominated a comet.
Without attending to the variety of opinions which philosophers and astronomers have entertained concerning the nature and use of comets, we may affirm, that they have been considered as alarming phenomena, displayed by the Divine Being to warn mankind of the near approach of some dreadful calamity, such as wars, pestilence, and famine. This opinion prevailed during the dark ages between the decline of the Roman empire, and the dawn of the Reformation. To this apprehension some of our modern poets have alluded in strong and descriptive language. Young says,
“Hast thou ne’er seen the comet’s flaming light?Th’ illustrious stranger passing, terror shedsOn gazing nations, from his fiery trainOf length enormous; takes his ample roundThrough depths of ether; coasts unnumber’d worldsOf more than solar glory; doubles wideHeaven’s mighty cape; and then revisits earth,From the long travel of a thousand years.”
“Hast thou ne’er seen the comet’s flaming light?
Th’ illustrious stranger passing, terror sheds
On gazing nations, from his fiery train
Of length enormous; takes his ample round
Through depths of ether; coasts unnumber’d worlds
Of more than solar glory; doubles wide
Heaven’s mighty cape; and then revisits earth,
From the long travel of a thousand years.”
Milton uses still greater strength of language when he compares his hero to a comet:
“Incensed with indignation, Satan stoodUnterrified, and like a comet burn’dThat fines the length of Ophiucus hugeIn the arctic sky, and from his horrid hairShakes pestilence and war.”
“Incensed with indignation, Satan stood
Unterrified, and like a comet burn’d
That fines the length of Ophiucus huge
In the arctic sky, and from his horrid hair
Shakes pestilence and war.”
Similar ideas are finely expressed by Savage: