Or when, compelled, it flies the torrid zone,
And shoots by worlds unnumbered and unknown;
By worlds, whose people, all aghast with fear,
May view that minister of vengeance near!
Till now, the transient glow, remote and lost,
Decays, and darkens 'mid involving frost!
Or when it, sunward, drinks rich beams again,
And burns imperious on th' ethereal plain,
The learned-one, curious, eyes it from afar,
Sparkling through night, a new illustrious star!

Amid the radiant orbs,

SAVAGE.

That more than deck, that animate the sky,
The life-infusing suns of other worlds;
Lo! from the dread immensity of space
Returning with accelerated course,
The rushing comet to the sun descends;
And as he sinks below the shaded earth,
With awful train projected o'er the heavens,
The guilty nations tremble. But, above
Those superstitious horrors that enslave
The fond sequacious herd, to mystic faith
And blind amazement prone, th' enlightened few
Whose godlike minds philosophy exalts,
The glorious stranger hail. They feel a joy
Divinely great; they in their powers exult,

That wondrous force of thought, that, mounting, spurns
This dusky spot, and measures all the sky;
While, from his far excursion through the wilds
Of barren ether, faithful to his time,
They see the blazing wonder rise anew,
In seeming terror clad, but kindly bent
To work the will of All-sustaining Love:
From his huge vapoury train, perhaps, to shake
Reviving moisture on the numerous orbs,
Through which his long ellipsis winds; perhaps,
To lend new fuel to declining suns,

To light up worlds, and feed th' eternal fire.

THOMSON.

When the terrors, which superstition and astrology formerly excited, had fled before the dawn of philosophy; when Newton, unfolding the system of the universe, had described the laws by which the motions of comets are directed, and Halle

had carried the theory of his illustrious predecessor to a high degree of certitude and perfection, their discoveries gave rise to a new kind of anxiety and apprehension. It was feared, that some of the comets, which move in all directions through the different regions of our planetary system, might, some time or other, meet with our earth in its course; and it was supposed that some rencounters may have already happened, and produced the revolutions of which the vestiges are to be found in several parts of our globe. Thus, Whiston considered the general flood as an inundation produced by the tail of a comet, and supposed that the universal conflagration will be occasioned by the earth's meeting with one of those bodies on its return from the Sun. Maupertuis imagined, that the tails of comets, by mixing their exhalations with our atmosphere, might have a noxious influence upon the health of animals and the growth of plants: he farther apprehended, that their attraction might, some time or other, oblige our globe to change its orbit, and to revolve about one of them in the character of a satellite, or, at least, expose it to more violent vicissitudes of heat and cold than it experiences at present. But these terrors are merely visionary, and have been refuted in an essay on this subject, by M. Dionis du Sejour. This work, which contains the best theory of comets hitherto published, has the double merit of having given new degrees of perfection and improvement to the science of astronomy, and of calming the fears and apprehensions of mankind, by showing, that we have absolutely little or nothing to fear from those flaming bodies, which ignorance and superstition have rendered so terrible.

Comets, according to Sir Isaac Newton, are

Essai sur les Comets en général, &c. Paris, 1775,

compact, solid, fixed and durable bodies: in one word, a kind of planets; which move in very oblique and eccentric elliptical orbits, every way with the greatest freedom; persevering in their motions, even against the course and direction of the planets and their tail is a very thin slender vapour emitted by the head or nucleus of the comet, ignited or heated by the sun.

From the lights which this great philosopher has thrown upon this abstruse part of astronomy, there is reason to hope that succeeding astronomers will carry it to the greatest degree of perfection. But, although we are indebted to him for a true theory of the motion of the comets, yet, with respect to the formation of their tails, and the uses for which these great bodies are intended, his opinions have been controverted. Dr. Hamilton, in particular, in his Philosophical Essays, controverts Sir Isaac's opinion. He asserts, from a view of the phenomena of a comet, that the matter which constitutes its tail is not an illuminated vapour, but a self-shining substance, which, in all positions of the comet, and whatever be the direction of its motion, whether toward or from the sun, is thrown off from its dark hemisphere, in a direction opposite to the sun, a short time before and after its perihelion, or nearest approach to that luminary. He finds, moreover, in the aurora borealis, a matter which greatly resembles it in appearance, its situation with regard to the sun and to the body whence it flows, as well as in the nature of its substance, so far as it is known to us: for the aurora borealis is likewise a rare and lucid substance, thrown off in a direction nearly opposite to the sun, from the dark hemisphere of the earth; tending toward the zenith of the spectator, or the vertex of the earth's shadow; rising principally from the northern part of the earth'

mosphere, and most frequently visible while the sun is passing through the southern signs, and the earth moving from the autumnal to the vernal equinox, through that half of its orbit which is nearest to the sun; and, lastly, not intercepting, in any sensible degree, the light of the fixed stars: so that, to a spectator placed at a considerable distance from the earth, and shaded from the sun's light, it must appear as a tail to the earth; small, indeed, in proportion to the earth's diameter, but in its direction, situation, transpaparency, and lucid appearance, resembling that of

a comet.

Abbé Mann, a learned Englishman, long resident at Brussels, has likewise shown, by unanswerable arguments, that there is a manifest and perfect analogy between the tails of these great and luminous bodies and the aurora borealis ; hence he concludes, that they both proceed from the same principle, and are formed of the same matter; that they are emanations of the electrical fluid from their respective bodies, and that this fluid often becomes a phlogiston, by the heterogeneous mixture which it carries along with it in this emanation, which accounts for the different colours and other circumstances in these meteors. 'As electrics (says the Abbé), when sufficiently heated, become conductors of the electrical fluid, and yield emanations of it in proportion to the quantity they naturally contain, this is precisely the case with the earth and the comets in their perihelia. The approach of the comets to the sun, and the superabundant degree of heat which they receive from this approach, dispose them to send forth a proportionable part of the electrical fluid, whose emission produces all the phenomena we observe in the tails of the comets, the auroræ boreales, and several electrical experiments; these

phenomena, therefore, have the same cause, and one common principle. In the recess of the comet and its increasing distance from the sun, this visible emission of electrical matter diminishes gradually, and, at last, totally disappears; and instead of being an electrical conductor, which it was in its perihelion, it attracts the fluid, is charged with it anew, and thus becomes electric until its approach to the sun, and the heat it acquires thereby, change it again into a conductor 1.

From the prodigious activity of the electrical fluid, its tendency to escape from the bodies which contain it, and to diffuse itself in the vast planetary regions, which come the nearest to void space, the ingenious Abbé draws some conjectures relative to the uses and the end which comets may serve in the planetary system. He thinks that comets are real electrical bodies designed to collect the electrical fluid, which has escaped from the planets: that the comets, heated by their approximation to the sun, communicate this fluid anew to the planets; and thus the perpetual circulation of this active fluid, so necessary to the great whole, is maintained and renewed incessantly; and that the operations of nature in the planetary system are carried on in a manner analogous to what we constantly observe and experience in the perpetual circulations of our at mosphere, where winds, vapours, and exhalations, rise and float; then return to us in rain, snow, and fulminating explosions; and then, again, are exhaled and raised anew. Every thing (he ju

• Memoir concerning Electrical Fire, &c. in Memoirs of the Academy at Brussels, vol. ii. Many other specula tions on the nature of comets are given in Dr. O. Gregory's Astronomy, and in M. Lambert's Letter on Cosmogony. See also Time's Telescope for 1814, p. 317.