For thousands of years Science itself remained enthralled by these delusive appearances, until at length the master-mind of Copernicus reduced our planet to the rank of an humble follower of that sun which it had so long appeared to rule.

This great man first convincingly proved that the sun does not revolve round the earth, but that we and all the planets circle round the sun; and that the earth, by turning on her axis every twenty-four hours from west to east, produces that apparent movement of the starry heavens from east to west which had deceived all previous astronomers. Where formerly darkness and error prevailed, and the most ingenious and complicated hypotheses had been unable to explain the intricate motions of the planets, the mystery was now solved at once in the clearest and most simple manner.

Building still further on the Copernican system, the illustrious Kepler next showed that the planets do not move in circles but in ellipses round the sun, and discovered the laws which regulate the swiftness and proportions of their orbits. Twelve years after this great man's death our immortal Newton was born, who proved that the movements of all the celestial bodies flow from the supreme law of universal gravitation, or the mutual attraction of bodies according to the proportion of their masses and distances.

By means of this fundamental law-which regulates the movements of the stars as well as the fall of terrestrial bodies, the course of waters, the motions of the pendulum, and the direction. of the load-line-it was now possible to solve many most difficult problems, which until then had baffled the sagacity of the greatest mathematicians and astronomers, to explain the precession of the equinoxes, to determine the weight and the masses of the various bodies of the solar system, and finally to calculate the perturbations resulting from the mutual attractions of the planets.

The word perturbation might possibly lead us to fear, that at a period however remote the laws which maintain the planets in their course might ultimately be overcome by counteracting forces, and an irreparable catastrophe be the consequence; but the calculations of Laplace have proved that all alarms on this subject are perfectly groundless, for the planetary perturbations are as subject to eternal laws as all the other motions of the

RISE OF ASTRONOMICAL SCIENCE.

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heavenly bodies; they never exceed a certain limit, they mutually correct each other, and cannot possibly become dangerous. Thus, by an admirable mechanism worthy of the Supreme Architect of worlds, even the deviations of the planets contribute to the eternal harmony of the spheres.

When Herschel discovered Uranus, that dim planet, which receives the faint rays of the sun from a distance of 1,600,000,000 geographical miles, it was supposed that the utmost limits of our solar system had been attained, and that beyond must begin the vast solitudes which separate the dominions of our sun from those of the nearest fixed star. But Uranus showed perturbations in his path, which could not be accounted for by the attraction of Saturn, and could therefore only be ascribed to an unknown planet. The calculations of Le Verrier determined the position and the mass of this new celestial body; and scarcely had he pointed out the spot where, according to all probability, it must be revolving through space, than the telescope of the Berlin astronomer Galle verified the accuracy of his statements, and discovered Neptune, circulating as a star of the eighth magnitude, 2,800,000,000 miles from the sun.

Truly a splendid triumph of mathematical science, a magnificent victory of the human mind, thus to calculate the existence of an unknown world, and to see, as it were by the light of reason, what no human eye had ever beheld!

Possibly other planets may still roll beyond Neptune, which perhaps no telescope will ever be able to detect; but from the perturbations they may cause, their existence will be as evident as if we could follow them on their lustrous path.

Besides the planets and moons and numerous comets, a vast number of smaller planetary bodies, partly disseminated, partly grouped in annular zones, revolve on elliptic orbits round the sun. When these small planetary bodies come within the sphere of the earth's attraction, they obey its influence, and, darting down, give rise to the phenomena of shooting-stars and meteoric stones.

On a bright night twenty minutes rarely pass, at any part of the earth's surface, without the appearance of at least one meteor. At certain times (the 12th of August and the 14th of November, when in all probability our earth crosses the orbit of one of those annular zones) they appear in enormous

numbers. During nine hours of observation in Boston, when they were described as falling like snowflakes, 240,000 meteors were calculated to have been observed. The number falling in a year might perhaps be estimated at hundreds or thousands of millions, and even these would constitute but a small portion of the total crowd of asteroids that circulate round the sun. As these bodies, while obeying the earth's attraction, traverse our atmosphere with planetary velocity, they would no doubt cause a terrible bombardment, and from their vast numbers render our planet absolutely uninhabitable, if their very speed had not been made the means of neutralising their otherwise disastrous effects: for, raised to incandescence by the atmospheric friction engendered by this enormous velocity of from eighteen to thirtysix miles a second, by far the greater portion of the aërolithes are dissipated by heat, and a small number only reaches the surface of the earth under the solid form of meteoric stones.

Interesting by their celestial origin, these masses are still more so as the only tangible and ponderable proofs we possess of the material existence of a world beyond our own--as teaching us that the substances of which our earth is composed exist also beyond its limits: for the chemist finds the meteoric stones composed of iron, nickel, cobalt, silica, aluminium, and other terrestrial elements, nor do they contain a single atom of any substance that is unknown to us on earth. This circumstance sufficed to render it very probable that our whole solar system has been constructed of identical materials; but the wonderful researches of Bunsen and Kirchhof have raised probability to certainty, by proving that sodium, calcium, magnesium, chromium, iron, and other metals are constituents of the solar atmosphere and of the sun's central orb.*

However vast the scale of our planetary system, however incapable our imagination may be to grasp its immensity, it still forms but a minute portion even of the visible universe; for how insignificant in point of numbers, size, and distance are all the satellites revolving round our sun, in comparison to the countless hosts of the sidereal heavens! So enormous are their distances, that the immense diameter of the earth's orbit, as

* The reader will find an excellent account of the experiments which led to this brilliant discovery in Professor Tyndall's admirable Lectures on Heat, pp. 408-415.

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seen from them, is only an indivisible point; and it is only within the last few years that instruments of a precision unknown to former ages have at length brought a small number of them within the reach of human calculation. In these immense regions of space solar orbits are too small to serve as a unity of measure; we are obliged to travel on the wings of light, which in a second leaves 200,000 miles behind, to be able to express, in a few numbers, distances which exceed the utmost limits of our conception.

A ray of light emitted from our earth would require three years and a half to reach the nearest fixed star; twenty years long it would have to dart through the fields of ether before it reached Sirius, and thirty years would have to pass before it rested on the Polar Star.

Thus the distances of about thirty of the nearest fixed stars have been measured; but the remaining thousands which we are able to see with the naked eye, and the millions which the telescope reveals to our gaze, roll on at such immense distances from our planet, that most probably no progress of astronomical science will ever be able to bridge over the intervening gulf. A reduction of stellar distances to a smaller scale will enable us to form some faint idea of the enormous difficulties of their calculation, and of the astonishing perfection of our instruments. Supposing the sun to be of the size of an orange, and placing it in the centre of the dome of St. Paul's, our pea-sized earth will then be performing its orbit within the circumference of the dome, while Neptune will be moving in the vicinity of the Bank, and many of the comets extending their vagrant excursions as far as Charing Cross. From these proportional distances we may easily conceive how, the diameter of the cathedral dome (which is here supposed to be the diameter of the earth's orbit) being known, it must be comparatively easy to measure all the angles necessary to calculate the distances of Neptune or any other planet: but when we come to consider that, according to the given proportions, the nearest fixed star would be sending us its light from the vast distance of St. Petersburg, then indeed we must be astonished at the perfection of the instruments which from so narrow a basis have been able to measure the allbut-imperceptible inclinations of the angles verging towards that distant world.

Before Bessel made the first successful attempt to determine the distance of a fixed star, Sir John Herschel had already taken the first steps towards the conquest of the sidereal heavens. Through telescopes of an increasing range, he saw with their growing power the number of the stars increase that presented themselves before his field of vision, and thus gained a measure for the form and the dimensions of the stellar system to which our sun with all his satellites belongs.

This amazing cluster of worlds-this our 'world-island,' as it has been appropriately called by Humboldt, consisting of all the constellations seen with the naked eye, and of the unnumbered stars that glimmer in the Milky Way-is of a lenticular, flattened, oblong, or elliptic form, and swims like a prodigious archipelago in the unmeasured realms of space. We know the immense distances that separate us from the nearest fixed stars, and can thus form a faint conception of the vast dimensions of a group composed (according to Herschel) of at least twenty millions of self-luminous stars. It has been calculated that a ray of light would require at least six thousand years to measure it from end to end, and fourteen hundred years to traverse it in its breadth. But even this amazing group of stars, vast and colossal beyond the bounds of human imagination, forms but a point in the universe, for on all sides similar clusters are seen looming out of the depths of the skies at distances to which that of Sirius from the earth dwindles down to one of our terrestrial measures. Many of these clusters, which are either entirely invisible to the naked eye, or appear only as nebular spots on the dark background of the celestial vault, require Lord Rosse's great telescope to be dissolved into their component stars; while others resist even this powerful test, and continue to appear as specks of mere luminous matter.

Hitherto it was supposed that the immensity of their distances alone prevented them from being dissolved; but the true nature of some of them at least has been fully established by recent investigations, which, by extending Bunsen's and Kirchhof's solar discoveries into the world of the fixed stars, have not only been able to prove that the glowing atmosphere of Aldebaran, for instance, contains quicksilver, and that of Sirius antimony, but that many of the nebulæ are in reality but immense gaseous bodies, which we may suppose to be new