18 COSMOS. 



ary nature of comets, and the deviation from the spherical 

 form observed in the figure of the earth.* Greek antiquity 

 is also replete with uranological presentiments of this na- 

 ture, which were realized in later times. 



In the development of thought on cosmical relations, of 

 which the main forms and epochs have been already enu- 

 merated, Kepler approached the nearest to a mathematical 

 application of the theory of gravitation, more than seventy- 

 eight years before the appearance of Newton's immortal 

 work, Principia Philosophies Naturalis. For while the 

 eclectic Simplicius only expressed in general terms " that 

 the heavenly bodies were sustained from falling in conse- 

 quence of the centrifugal force being superior to the inher- 

 ent falling force of bodies and to the downward traction ;" 

 while Joannes Philoponus, a disciple of Ammonius Hermeas, 

 ascribed the movement of the celestial bodies to " a primi- 

 tive impulse, and the continued tendency to fall ;" and while, 

 as we have already observed, Copernicus defined only the 

 general idea of gravitation, as it acts in the sun, as the center 

 of the planetary world, in the earth and in the moon, using 

 these memorable words, " Gravitatem non aliud esse quam 

 appetentiam quandam naturalem partibus inditam a divina 

 providentia opificis universorum, ut in unitatem integrita- 

 temque suam sese conferant, in formam globi coeuntes ;" 

 Kepler, in his introduction to the book De Stella MartisJ 

 was the first who gave numerical calculations of the forces 

 of attraction reciprocally exercised upon each other, accord- 

 ing to their relative masses, by the earth and moon. He 



* Bartholmess, torn, ii., p. 219, 232, 370. Bruno carefully collected 

 all the separate observations made on the celestial phenomenon of the 

 sudden appearance, in 1572, of a new star in Cassiopeia. Much dis- 

 cussion has been directed in modern times to the relation existing be- 

 tween Bruno, his two Calabrian fellow-countrymen, Bernardino Tele- 

 sio and Thomas Campanella, and the platonic cardinal, Nicolaus Krebs 

 of Cusa. See Cosmos, vol. ii., p. 310, 311, note. 



t " Si duo lapides in aliquo loco Mundi collocarentur propinqui in- 

 vicem, extra orbem virtutis tertii cognati corporis ; illi lapides ad simil- 

 itudinem duorum Magneticorum corporum coirent loco intermedio, qui- 

 libet accedens ad alterum tanto intervallo, quanta est alterius moles in 

 comparatione. Si luna et terra non retinerentur vi animali (!) aut alia 

 aliqua aequipollente, quselibet in suo circuitu, Terra adscenderet ad Lu- 

 nam quinquagesima quarta parte intervalli, Luna descenderet ad Ter- 

 rarn quinquaginta tribus circiter partibus intervalli; ibi jungerentur, 

 posito tamen quod substantia utriusque sit unius et ejusdem densitatis." 

 Kepler, A&tronomia nova, seu Physica ccclestis de Motibus Stella Mar- 

 tis, 1609. Introd., fol. v. On the older views regarding gravitation, 

 see Cosmos, vrl. ii., p. 310. 



