ANALOGY. 301 



alogies receives a salutary correction in the recently dis- 

 covered fact that the atmosphere of Uranus contains 

 hydrogen. Philosophers of the highest grade have not 

 stopped at these comparatively safe inferences, but have 

 speculated on the existence of living creatures in other 

 planets. Huyghens remarked that as we infer by analogy 

 from the dissected body of a dog to that of a pig and 

 ox or other animal of the same general form, and as we 

 expect to find the same viscera, the heart, stomach, lungs, 

 intestines, &c., in corresponding positions, so when we 

 notice the similarity of the planets in many respects, we 

 must expect to find them alike in other points 11 . He 

 even enters into an inquiry whether the inhabitants of 

 other planets would possess reason and knowledge of the 

 same sort as ours, concluding in the affirmative. Although 

 the power of intellect might be different, he considers that 

 they would have the same geometry if they had any at 

 all, and that what is true with us would be true with 

 them . As regards the sun, he wisely observes that every 

 conjecture fails. Laplace entertained a strong belief in 

 the existence of inhabitants on other planets. The benign 

 influence of the sun gives birth to animals and plants 

 upon the surface of the earth, and analogy induces us to 

 believe that his rays would tend to have a similar effect 

 elsewhere. It is not probable that matter which is here 

 so fruitful of life, would be sterile upon so great a globe 

 as Jupiter, which, like the earth, has its days and nights 

 and years, and changes which indicate active forces. Man 

 indeed is formed for the temperature and atmosphere in 

 which he lives, and, so far as appears, could not live upon 

 the other planets. But there might be an infinity of 

 organizations relative to the diverse constitution of the 

 bodies of the universe. The most active imagination can- 



n ' Cosmotheoros ' (1699), p. 17. 

 Ibid p. 36. 



