366 



INDUCTION. 



resemble, than among things between 

 which we know of no resemblance. 



For example, I might infer that 

 there are probably inhabitants in the 

 moon, because there are inhabitants 

 on the earth, in the sea, and in the 

 air ; and this is the evidence of ana- 

 logy. The circumstance of having 

 inhabitants is here assumed not to 

 be an ultimate property, but (as is 

 reasonable to suppose) a consequence 

 of other properties ; and depending, 

 therefore, in the case of the earth, on 

 some of its properties as a portion of 

 the universe, but on which of those 

 properties we know not. Now the 

 moon resembles the earth in being a 

 solid, opaque, nearly spherical sub- 

 stance, appearing to contain, or to 

 have contained, active volcanoes ; re- 

 ceiving heat and light from the sun 

 in about the same quantity as our 

 earth ; revolving on its axis ; com- 

 posed of materi-als which gravitate, 

 and obeying all the various laws re- 

 sulting from that property. And I 

 think no one will deny that if this 

 were all that was known of the moon, 

 the existence of inhabitants in that 

 luminary would derive from these 

 various resemblances to the earth a 

 greater degree of probability than it 

 would otherwise have : though the 

 amount of the augmentation it would 

 be useless to attempt to estimate. 



If, however, every resemblance 

 proved between B and A, in any 

 point not known to be immaterial 

 with respect to m, forms some addi- 

 tional reason for presuming that B 

 has the attribute m, it is clear, t 

 contra, that every dissimilarity which 

 can be proved between them fur- 

 nishes a counter-probability of the 

 same nature on the other side. It is 

 not indeed unusual that different 

 ultimate properties should, in some 

 particular instances, produce the same 

 derivative property ; but on the whole 

 it is certain that things which differ 

 in their ultimate properties will 

 differ at least as much in the aggre- 

 gate of their derivative properties, 

 aii(} that the differences which are 



unknown will on the average of 

 cases bear some proportion to those 

 which are known. There will, there- 

 fore, be a competition between the 

 known points of agreement and the 

 known points of difference in A and 

 B ; and according as the one or the 

 other may be deemed to preponde- 

 rate, the probability derived from 

 analogy wull be for or against B's 

 having the property m. The moon, 

 for instance, agrees with the earth in 

 the circumstances already mentioned ; 

 but differs in being smaller, in having 

 its surface more unequal, and ap- 

 parently volcanic throughout, in hav- 

 ing, at least on the side next the 

 earth, no atmosphere sufficient to re- 

 fract light, no clouds, and (it is there- 

 fore concluded) no water. These 

 differences, considered merely as 

 such, might perhaps balance the re- 

 semblances, so that analogy would 

 afford no presumption either way. 

 But considering that some of the 

 circumstances which are wanting on 

 the moon are among those which, on 

 the earth, are found to be indispens- 

 able conditions of animal life, we may 

 conclude that if that phenomenon 

 does exist in the moon, (or at all 

 events on the nearer side,) it must be 

 as an effect of causes totally different 

 from those on which it depends here; 

 as a consequence, therefore, of the 

 moon's differences from the earth, not 

 of the points of agreement. Viewed 

 in this light, all the resemblances 

 which exist become presumptions 

 against, not in favour of, the moon's 

 being inhabited. Since life cannot 

 exist there in the manner in which it 

 exists here, the greater the resem- 

 blance of the lunar world to the 

 terrestrial in other respects, the less 

 reason we have to believe that it can 

 contain life. 



There are, however, other bodies in 

 our system, between which and the 

 earth there is a much closer resem- 

 blance, which possess an atmosphere, 

 clouds, consequently water, (or some 

 fluid analogous to it,) and even give 

 strong indications of snow in their 



