In th' Arctic sky, and from his horrid hair
Shakes pestilence and war;"—

where, also, you find an allusion to the superstitious belief in mischievous influences from comets.

But this hair, or spreading light, of a comet, is seen, at different times, in very different forms and directions, and is therefore very differently named. You know the nursery rhyme

"I saw a peacock with a fiery tail;"

and here, the tail, otherwise called the train, is the name given to the hair or light. But the same light is otherwise called the beard; and thus comets are sometimes spoken of, not as tailed stars, but as bearded stars.

The reason why the spreading light, or spreading hair, of a comet, is sometimes called its tail, and sometimes its beard, is (as I have now led you to guess) that it sometimes goes before, and at other times behind; and it is the cause

of this change in the direction that I am now going to explain. A comet is always either approaching the sun, or else going from it; but, whichever of these two ways it moves, its spreading light is always upon that side which is turned from the sun, and not upon the side nearest to it. That is, it never points toward the sun, but always away from it; so that it sometimes comes before the comet, and sometimes follows after.

For the present, you must suppose that every comet is in itself a globe or ball, like the sun or moon, or like any other star or planet; including the earth, our own ball or globe. Now these balls or globes of the stars, and planets, and comets, are likened, in our imagination, to human or other heads; though, in respect of a comet, the head is also called the nucleus, or kernel, or that essential body, or comet properly so called, to which the rest belongs. See, then, as a comet goes round the sun, with its hair or

spreading light always pointing away from the sun, how various its position will seem to us to

be, in respect of its own nucleus or head. For, here, a being the sun, B a comet approaching

the sun, and c the same comet departing from it; then, the comet as represented at B will be said to have a tail, or hair, or tail or train of light behind its nucleus, or head, or body; while the same comet, as represented at c, will be said to be bearded, or to have hair projecting in front of the nucleus, head, or body, or chin. For, to our eyes, the first will seem to follow the comet, and the second to come before it.

Nor are these two aspects the only ones in which the same comet, in different parts of its course, can show itself to us. We may see it, (as between B and c

at D and E, or at any point and c and B), foreshortened more or less, and showing neither at one end nor the other its spreading hair or light behind it, but (more or less) it will seem to be around it; like the rays of the sun around the sun, or like the tail of a peacock, in the second of the following three positions for, here, a and c will represent

the two side views of the same comet, and B the front; while, if we had a back view of the same bird, with its head or body visible through

a transparent tail; then, these front and back views (B and its companion) would answer to the figures D and E in my diagram, and show us when the spreading and hair or light of the comet (spreading much wider, and higher and lower, than the head or body of the comet) would seem to surround it, like what we call a glory, or like the constant hair or rays of the