INTUODUCTION. 21 



the liurnaii race may there present. The reader might sup 

 pose he were peiiismg Kepler's Somniuon Astronojnicum, oi 

 Kircher's Iter Extaticus. As Ilnygens, hke 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 mhahitants in the moon than of those in the remoter 

 pLanets, which he assumes to he " surrounded with vapors 

 and clouds." 



The immortal author of the Pliilosophice Is'aturalis Prin- 

 cipia Matliematica (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- 

 ical 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 wdiich 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 simxplicity 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 aqiiis carei'e et a6re : IManum similitudinem ia Luna nul- 

 1am reperio. Nam regiones planas qucB montosis multo obscuriores 

 sunt, quasque vulgo pro maribus haberi video et oceanoiizra nomiuibna 

 insiguiri, iu his ipsis, longiore telescopio iuspectis, cavitates exiguas iii- 

 esse comperio rotundas, umbris intus cadentibus ; quod maris siipei-fi- 

 ciei convenire nequit; turn ipsi campi illi latiores nou prorsus a^quabi- 

 lem superficiem prsferuut, cum diligeutius eas intuemur. Quod circa 

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

 quam qua? est partibus asperioribus in quibus rursus qua^dam viridiori 

 liimine caeteras prgecellunt." — Hugenii Cosynotkeoros, 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 Jovialiura 

 miitabili facie cognoscitur" (lib. i., p. G9). These dreams of Huygens 

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

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

 Kant, iu his admirable -work Jllgemeine Naturgeschichte und Theorii 

 det Himmels, l755 (s. 173-192). 



t See Laplace {des Oscillations de V Atmoiplicre, dn jinx Solaira et 

 Lnnaire) iu the Mecaniqve Celeste, livrt; iv., and iu the Exposition, dn 

 a.yU. dn Monde, 1S24, p. '.391-29o. 



