OF THE COSMOS. INTRODUCTION. 21 



the Moon neither air nor water, ( 37 ) he finds the supposed 

 existence of lunar men present to him still greater diffi- 

 culties than that of the inhabitants of the remoter planets 

 " rich in clouds and vapour." 



The immortal author of the Philosophise Naturalis Prin- 

 cipia Mathernatica, succeeded, by the assumption of a single 

 all- governing fundamental moving force, in embracing the 

 whole uranological portion of the Cosmos in the causal 

 connection of its phenomena. Newton first raised physical 

 astronomy to a mathematical science, and made it the solu- 

 tion of a great problem of mechanics. The quantity of 

 matter in each heavenly body gives the measure of its at- 

 tracting force, a force which acts in the inverse ratio of the 

 square of the distance, and determines the magnitude of the 

 perturbing actions which not only the planets, but all the 

 heavenly bodies in space, exert upon each other. But the 

 Newtonian theorem of gravitation, so admirable for simpli- 

 city and generality, is not limited in its cosmical application 

 to the sphere of uranology ; it governs also terrestrial phse- 

 nomena in directions still partly uninvestigated ; it gives 

 the key to periodic movements in the ocean and in the 

 atmosphere, ( 3S ) to the solution of problems of capillarity, 

 endosmose, and many chemical electro -magnetic and organic 

 processes. Newton himself ( 39 ) already distinguished the 

 " attraction of mass," as it manifests itself in all celestial 

 bodies and in the phaenomena of the tides, from " molecular 

 attraction," which acts at infinitely small distances and in 

 the closest contact. 



Thus among all human efforts to reduce all variations 

 taking place in the world known to us through our senses 

 to a single fundamental principle, the doctrine of gravita- 



