looked upon, as the most certain, and best established of the sciences.

"We also know, that every visible object appears less in magnitude as it recedes from the eye. The lofty vessel, as it retires from the coast, shrinks into littleness, and at last appears in the form of a small speck on the verge of the horizon. The eagle, with its expanded wings, is a noble object: but when it takes its flight into the upper regions of the air, it becomes less to the eye, and is seen like a dark spot, upon the vault of heaven. The same is true of all magnitude.” "The heavenly bodies appear small to the eye of an inhabitant of this earth only from the immensity of their distance. When we talk of hundreds of millions of miles, it is not to be listened to as incredible. For remember that we are talking of those bodies which are scattered over the immensity of space, and that space knows no termination. The conception is great and difficult, but the truth is unquestionable. By a process of measurement which it is unnecessary at present to explain, we have ascertained first the distance, and then the magnitude, of some of those bodies which roll in the firmament; that the sun which presents itself to the eye under so diminutive a form, is really a globe, exceeding, by many thousands of times, the dimensions of the earth we inhabit; that the moon itself has the magnitude of a world; and that even a few of those stars which appear like so many lucid points to the unassisted eye of the observer expand into large circles upon the application of the telescope; and are some of them much larger than the ball which we tread upon, and to which we proudly apply the denomination of the universe."

"Did the discoveries of science stop here, we have enough to justify the exclamation of the Psalmist, 'What is man, that thou art mindful of him; or the son of man, that thou shouldst deign to visit him?" They widen the empire of creation far beyond the limits which were formerly assigned to it. They give us to see that yon Sun, throned in the centre of his planetary system, gives light and warmth, and the vicissitude of seasons, to an extent of surface several hundred times greater than that of the earth which we inhabit. They lay open to us a number of worlds, rolling in their respective circles around this vast luminary; and prove that the ball which we tread upon, with all its mighty burden of oceans and continents, instead of being distinguished from the others, is among the least of them; and from some of the more distant planets, would not occupy a visible point in the concave of their firmament. They let us know, that though this mightly earth, with all its myriads of people, were to sink into annihilation, there are some worlds, where an event so awful to us, would be unnoticed and unknown, and others where it would be nothing more than the disappearance of a little star which had ceased from its twinkling. We should feel a sentiment of modesty at this just but humiliating representation. We should learn not to look on our earth as the universe of God, but one paltry and insignificant portion of it; that it is only one of the many mansions which the Supreme Being has created for the accommodation of His worshippers, and only one of the many worlds rolling in that flood of light, which the Sun pours around him to the outer limits of the planetary system."

221

CHAPTER XI.

COMETS-HISTORICAL NOTICES OF-THEORIES AND PHENOMENA OF. ORBITS OF PLANETS AND OF COMETS. COMETS OF HALLEY, ENCKE, AND BIELA. UNDULATORY TAILS OF

THEORY OF LIGHT.

DIMENSIONS OF THE

COMETS.

COMETS.

Amid the radiant orbs,

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 shading 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, the 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, which 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.

THERE are but few objects in creation, which excite more wonder and interest than those comets which are accompanied by long trains, or tails, of luminous ethereal matter. In the early ages, the most extravagant superstition was connected with the appearances of these visitors: whole nations seemed to feel as if they were under a terrible infliction from heaven; and an indescribable awe, which is a general attendant on ill-understood or misunderstood phenomena, prevailed on the subject. Though this feeling has now in great measure passed away, they are still objects of wonder to the uninstructed; and even those who are best informed on the subject, have little better than conjecture to offer respecting them.

The principal reasons why comets do not admit of being considered as part of the solar system in the same rank as the planets, is, that they cannot be traced through their orbits with that certainty which the planets can, and that their appearances vary so greatly at different times: it has been even doubted by some whether a comet has any solid body at all, like other members of the solar system.

If we are to believe the narrations of early writers, it would appear that comets were once seen, greatly exceeding in size those which have appeared of late years; from whence it seems that the whole tribe of comets deteriorates, as if, being of an unsubstantial nature, they were gradually wearing away in the course which they describe in space. In the year 130 B. C., a comet was seen so large that it appeared to have the same diameter as the Sun. In the year 60 B. c. a large comet was seen very distinctly near the Sun, which happened at the time to be totally eclipsed, and