640 THE PRINCIPLES OF SCIENCE. [CHAP. 



in many respects, we must expect to find them alike in 

 other respects. 1 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. 2 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 organisations relative to the diverse 

 constitutions of the bodies of the universe. The most 

 active imagination cannot form any idea of such various 

 creatures, but their existence is not unlikely. 3 



We now know that many metals and other elements 

 never found in organic structures are yet capable of form- 

 ing compounds with substances of vegetable or animal 

 origin. It is therefore just possible that at different tem- 

 peratures creatures formed of different yet analogous com- 

 pounds might exist, but it would seem indispensable that 

 carbon should form the basis of organic structures. We 

 have no analogies to lead us to suppose that in the absence 

 of that complex element life can exist. Could we find 

 globes surrounded by atmospheres resembling our own in 

 temperature and composition, we should be almost forced 

 to believe them inhabited, but the probability of any ana- 

 logical argument decreases rapidly as the condition of a 

 globe diverges from that of our own. The Cardinal 

 Nicholas de Cusa held long ago that the moon was 



1 Cosmotheoros (1699), p. 17. 2 Ibid. p. 36. 



3 System of the World, vol. ii. p. 326. Essai Philosophique. p. 87. 



