There is, however, in the showings of science, a more serious danger than any of these. Comets were once regarded as most terrific objects, but only in a superstitious way, perplexing nations with fear of change, and shaking pestilence from their horrid hair. During an intermediate enlightened time, these notions passed away; and we have even come to think, that such a visitant of our skies may exercise a beneficial influence. We at least recollect when old gentlemen, after dinner, brightened up at the mention of 'claret 1811,' merrily attributing the extraordinary merits of the liquor to the comet of that year. But comets, in the cool eye of modern science, are not without their terrors. Crossing as they often do the paths of the planets in their progress to and from their perihelia, it cannot but be that they should now and then come in contact with one of these spheres. One, called Lexell's, did come athwart the satellites of Jupiter in 1769, and once again in 1779, so as to be deranged in its own course. It made, indeed, no observable change in the movements of the Jovian train, being of too light a consistence for that; but can we doubt, that it might nevertheless seriously affect the condition of their surfaces, and especially any animal life existing thereon? This very comet, on the 28th of June 1770, passed the earth at a distance only six times that of the moon. There is another called Biela's, which revisits the sun every six years, or a little more; and this busy traveller actually crossed our orbit in 1832, only a month before we passed through the same point in space! Another, which made a grand appearance in the western sky in March 1843, would have involved us in its tail, if we had been only a _fortnight_ earlier at a particular place! Rather fine shaving that in the celestial economics. Now, if we consider that as many as eight comets have been observed telescopically in a single year (1846), we must see that the chance of a collision of this kind is not quite so small as to be unworthy of regard. If it be true that there are thousands of comets, all of which make periodical visits to the near neighbourhood of the sun, it must be evident that the earth, being itself not far, comparatively speaking, from that luminary, must be rather liable as otherwise to a brush from one of these wanderers; and, indeed, the wonder is, that several thousand years should have passed without, so far as we know, any one such collision having taken place.