Although I do not think that the moon can be regarded as probably at present the abode of life, there are many reasons for studying in a work on other worlds the various relations she presents to us. In the first place, she subserves various useful purposes in the economy of our own earth; then there are circumstances in her appearance which suggest that at one time there may have been life upon her surface; and, lastly, she affords us the only information we have concerning the probable relations presented by the noble systems of moons which circle around Jupiter and the other planets outside the orbit of the asteroids.

Now, with regard to the present habitability of the moon, it may be remarked that we are not justified in asserting positively that no life exists upon her surface. Life has been found under conditions so strange—we have been so often mistaken in assuming that here certainly, or there, no living creatures can possibly exist—that it would be rash indeed to dogmatise respecting the state of the moon in this respect.

Still, in the case of the moon we have relations wholly different in character from those we have hitherto had to consider. We no longer have to deal with a question of the various degrees of heat and cold, of atmospheric rarity or density, and the like, but with relations which do not in the slightest degree resemble those we are familiar with on earth.