INTRODUCTION. 21 



the human race may there present. The reader might sup- 

 pose he were perusing Kepler's Somnium Astronomicum, or 

 Kircher's Iter Extaticus. As Huygens, like the astronomers 

 of our own day, denied the presence of air and water in the 

 moon,* he is much more embarrassed regarding the exist- 

 ence of inhabitants in the moon than of those in the remoter 

 planets, which he assumes to be " surrounded with vapors 

 and clouds." 



The immortal author of the Philosophies Naturalis Prin- 

 cipia Mathematica (Newton) succeeded in embracing the 

 whole uranological portion of the Cosmos in the causal con- 

 nection of its phenomena, by the assumption of one all-con- 

 trolling fundamental moving force. He first applied phys- 

 ica^astronomy to solve a great problem in mechanics, and 

 elevated it to the rank of a mathematical science. The 

 quantity of matter in every celestial body gives the amount 

 of its attracting force ; a force which acts in an inverse ra- 

 tio to the square of the distance, and determines the amount 

 of the disturbances, which not only the planets, but all the 

 bodies in celestial space, exercise on each other. But the 

 Newtonian theory of gravitation, so worthy of our admira- 

 tion from its simplicity and generality, is not limited in its 

 cosmical application to the uranological sphere, but com- 

 prises also telluric phenomena, in directions not yet fully 

 investigated ; it affords the clew to the periodic movements 

 in the ocean and the atmosphere,! and solves the problems 

 of capillarity, of endosmosis, and of many chemical, elec- 



* " Lunam aquis carere et afire : Marium sirnilitudinem in Luna nul- 

 lam reperio. Nam regiones planas quae montosis multo obscuriores 

 sunt, quasque vulgo pro maribus haberi video et oceanorum nominibus 

 insigniri, in bis ipsis, longiore telescopio inspectis, cavitates exiguas in- 

 esse comperio rotundas, umbris intus cadentibus ; quod maris superfi- 

 ciei convenire nequit ; turn ipsi campi illi latiores non prorsus a?quabi- 

 lem superficiem prasferunt, cum diligentius eas intuemur. Quod circa 

 maria esse non possunt, sed materia constare debent minus candicante, 

 quam qua? est partibus asperioribus in quibus rursus quaedam viridiori 

 lumine casteras prascellunt." Hugenii Cosmotheoros, ed. alt. 1699, lib. 

 xi., p. 114. Huygens conjectures, however, that Jupiter is agitated by 

 much wind and rain, for "ventorum flatus ex ilia nubium Jovialium 

 mutabili facie cognoscitur" (lib. i., p. 69). These dreams of Huygens 

 regarding the inhabitants of remote planets, so unworthy of a man versed 

 in exact mathematics, have, unfortunately, been revived by Emanuel 

 Kant, in his admirable work Jllgemeine Naturgeschichte und Theorit 

 desHimmels, 1755 (s. 173-192). 



t See Laplace (des Oscillations de I'Atmotpkere, du Jinx Solaire et 

 Lunaire) in the Mecanique Celeste, livre iv., and in the Exposition, du 

 Syst. du Monde, 1824, p. 291-296. 



