ANALOGY. 89 



which can he shown to exist, affords ground for expecting 

 an indefinite number of other resemblances : the particular 

 resemblance sought will, therefore, be oftener found among 

 things thus known to resemble, than among things between 

 which we know of no resemblance.* 



For example, I might infer that there are probably inha- 

 bitants in the moon, because there are inhabitants on the earth, 

 in the sea, and in the air : and this is the evidence of analogy. 

 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 substance, appearing to contain, or to have 

 contained, active volcanoes ; receiving heat and light from the 

 sun, in about the same quantity as our earth ; revolving on its 

 axis ; composed of materials which gravitate, and obeying all 

 the various laws resulting 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, 



* There was no greater foundation for this than for Newton's celebrated con- 

 jecture tbat the diamond was combustible. He grounded his guess on the very 

 high refracting power of the diamond, comparatively to its density ; a pecu- 

 liarity which had been observed to exist in combustible substances ; and on 

 similar grounds he conjectured that water, though not combustible, contained 

 a combustible ingredient. Experiment having subsequently shown that in 

 both instances he guessed right, the prophecy is considered to have done great 

 honour to his scientific sagacity ; but it is to this day uncertain whether the 

 guess was, in truth, what there are so many examples of in the history of 

 science, a farsighted anticipation of a law afterwards to be discovered. The 

 progress of science has not hitherto shown ground for believing that there is 

 any real connexion between combustibility and a high refracting power. 



