18 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN 



conjectures respecting the movement of the fixed stars, 

 the planetary nature of comets, and the deviation of the 

 figure of the Earth from that of a perfect sphere. ( 30 ) Gre- 

 cian antiquity is also full of such uranological divinations, 

 which have been subsequently realised. 



In the development of thought respecting cosmical relations 

 of which the leading forms and epochs have been here enume- 

 rated, it was Kepler who, fully 78 years before the publication 

 of Newton's immortal work of the " Principia Philosophise 

 naturalis," came nearest to a mathematical application of 

 the doctrine of gravitation. Although the Eclectic Sim- 

 plicius expressed in a general manner that " the non-falling 

 of the heavenly bodies was caused by the centrifugal force 

 having the upper hand of the proper falling force, the down- 

 ward traction;" although John Philoponus, a disciple of 

 Ammonius, the son of Hermeas, ascribed the movements of 

 the heavenly bodies " to a primitive impetus and to the con- 

 tinued tendency to fall " and although Copernicus, as was 

 noticed in an earlier part of the present work, describes the 

 merely general idea of gravitation, as it acts in the Sun as 

 the centre of the planetary world, and in the Earth and 

 Moon, in these remarkable words : " Gravitatem non aliud 

 esse quam appetentiam quandam naturalem partibus inditam 

 a divina providentia opificis universorum, ut in unitatem 

 integritatemque suam sese conferant, in formam globi co- 

 euntes ;" yet it is ' in Kepler, in the Introduction to the 

 book "De Stella Martis," ( 31 ) that we first find numerical 

 quantities assigned to the attracting forces which the Earth 

 and the Moon exercise upon each other in the ratio of their 

 masses. It distinctly adduces the ebb and flow of the sea 

 ( 32 ) as a proof that the attracting power of the Moon, (virtus 



