directly interested — not for their own sake, but for the sake of their remote descendants — in the subject of the moon's present airless and waterless condition, regarded as the result of systematic processes of change. If we can ascertain what those processes may have been, and if we should find that similar processes are taking place, however slowly, on the earth, then the moon's present condition has in a sense the same sort of interest for us that a man in the full vigor of life might be supposed to find in the study of the condition of aged persons, if through some strange chance he had never had an opportunity of observing earlier the effects of old age upon the human frame. The inhabitant of earth who contemplates the moon's present wretched condition, may be disposed — like Lydia Van den Bosch when she saw Madame Bernstein's shaky hands and hobbling gait — to hope we "sha'n't be like her when we're old, anyhow;" but the probabilities are in favor of a young world following in the same path which those now old have followed, and so reaching the same condition. If the moon is really a much older world than the earth — and we have seen that in all probability she is — then she presents to us a picture of the condition which our earth will hereafter attain.
We had occasion in the article on the moon, referred to above, to notice the theory advanced by Frankland in this country respecting the way in which the lunar air and seas have been caused to disappear; but we did not then enter into any very careful discussion of that theory, our purpose leading us to consider other matters. But in this place the theory must occupy a larger share of our attention. In passing, we may remark that the originator of the theory was Seeman, the German geologist; but it was independently advanced by Frankland in England, Stanislas Meunier in France, and Sterry Hunt in America.
In the first place, it is to be noted that no other theory seems available. Of three others which have been advanced, only one, Hansen's, according to which the seas and atmosphere of the moon have been drawn by lunar gravity to the farther or unseen hemisphere of the moon, needs serious refutation. (The other two are Whiston's theory, that a comet carried off the lunar seas and air; and the theory — whose author is unknown to us — that the lunar seas, and later the lunar atmosphere, have been, frozen through the intensity of cold, to which, in the long lunar nights, the moon is exposed.) But this theory is no longer entertained by astronomers, simply because it has been shown that the peculiarity of the moon's shape which had suggested the theory has been found, first, to have no real existence; and, secondly, to be incapable, if it existed, of exercising the supposed effect.[1]
The theory independently advanced by the four students of science named above is simply this, that seas formerly existing on the surface of the moon have been gradually withdrawn into the moon's interior, and that a similar process, but chemical rather than mechanical, has led to the withdrawal of the greater portion of the air which formerly enveloped the moon's frame.
It may be well, first, to inquire whether the moon is likely to have had originally an atmosphere of considerable density and oceans of considerable extent. Supposing, for the sake of argument, that the materials of the moon's mass (including air and water) were originally proportioned as to quantity very much like those of our earth's mass, it is easily seen that the quantity of air above each square mile of the moon's surface, at the time when the moon had reached the stage of planetary development through which our earth is now passing, must have been very much less than
- ↑ The idea was that the moon, though nearly spherical, is somewhat egg-shaped, the smaller end of the egg-shaped figure being directed towards our earth. Now, while it is perfectly clear that on this supposition the greater part of the moon's visible half would be of the nature of a gigantic elevation above the mean level, and would therefore be denuded (or might be denuded) of its seas and the denser parts of the air formerly covering it, yet it is equally clear that all round the base of this monstrous lunar elevation the seas would be gathered together, and the air would he at its densest. But it is precisely round the base of this part of the moon, or, in other words, round the border of the visible lunar hemisphere, that we should have the best chance of perceiving the effects of air and seas, if any really existed; and it is because of the absolute absence of all evidence of the kind that astronomers regard the moon as having no seas and very little air. It is worthy of notice that Hansen's theory was anticipated by the author of that clever little pamphlet called "The Lunar Hoax," who places the human inhabitants (the Bat-men) in the regions near the edge of the lunar disc, on the strength of some such views as Hansen advanced a quarter of a century later. Recently the Chicago Times published several columns of lunar-hoax matter, purporting to be an account of observations made in France with a new and exceedingly powerful reflecting telescope. The observations made with this instrument showed a number of lunar folks, whose movements rendered it manifest that they were prisoners undergoing some kind of penal servitude, the visible lunar hemisphere being a sort of Botany Bay or Cayenne for lunar offenders, while the other hemisphere is a comfortable place of abode for good moon people. But what an unhappy state of things is here suggested! Conceive a world, one half of whose surface is required as an abode for its malefactors!
