Notices respecting New Books. 235 



side, let us consider " the analogy of our own planet." There are 

 two heavenly bodies in regard to the habitability of which we can 

 speak with tolerable certainty ; the one is the Earth, the other is the 

 Moon. If we knew the Earth alone, the argument of analogy would 

 lead to the conclusion that all the planets are inhabited ; if we knew 

 the Moon alone, the same argument would lead to the conclusion 

 that none are inhabited : two considerations which show that the 

 argument of analogy, when thus employed, proves nothing. 



When we descend to details, the negative argument becomes 

 lamentably strong. Let us put the case thus : — Suppose the Earth, 

 peopled as at present, to have the conditions of life on its surface 

 brought into conformity with those known to exist on the surface of 

 Saturn ; viz., suppose the length of the day to be reduced by more 

 than one-half, the length of the year increased thirtyfold, the heat 

 and light of the sun reduced to one- ninetieth of its present amount, 

 and extensive tracts of the regions on either side of the equator to 

 be exposed to eclipses lasting for several years (as men count years) 

 — suppose this to be done, and we may be pretty certain that all the 

 higher forms of life would be destroyed by the change, and this 

 irrespectively of any of the numerous adverse possibilities of which 

 we gave a specimen above. Of course it is possible that the laws 

 of the variability of species, and of natural selection (supposing such 

 laws to have any real existence) acting on the remaining lower forms, 

 might in time give rise to races of highly organized beings, totally 

 different from anything which we have seen or can conceive ; but 

 though this is possible, there is nothing to show that it would be so 

 in fact. 



Above we took it for granted that there is conclusive evidence 

 that the Moon is uninhabitable. Mr. Proctor has an elaborate note 

 of six closely printed pages on the Habitability of the Moon, which 

 in its way is really very curious. He very properly regards the 

 question as involved in the secondary question whether the Moon 

 has an atmosphere. To all appearance he would answer this ques- 

 tion in the negative, were his judgment not oppressed by "the ana- 

 logy of our planet." Accordingly, as the evidence will not allow 

 him to believe that there exists a gaseous atmosphere, he suggests 

 that it may have become solid. His notion is that the Moon has 

 become intensely cold, and that her surface is covered with glaciers — 

 not glaciers here and there, but that what we see on her surface is a 

 frozen ocean, hemmed in by frozen continents covered with glaciers — 

 ice everywhere — all her pleasant seas and rivers fast bound in iron 

 misery. And as though this were not enough, he goes on to 

 tell us that " it is conceivable that the Moon's mass may have be- 

 come so intensely cold that the atmospheric envelope, once clothing 

 it, has been condensed into the liquid, and thence into the solid 

 form " (p. 212). We have tried, but cannot conceive it. When we 

 remember that the temperature of the Earth's surface is determined 

 by the solar radiation, and not by the interior heat or cold, we can- 

 not help thinking that the same must be true of the Moon, and 

 therefore cannot conceive how the gases can ever have become 



