VI GENERAL SUMMARY 



Magnus, Imago Mundi of the Cardinal Pierre d'Ailly. Progress throngh 

 Giordano Bruno and Telesio. Clearness in the conceptions of gravitation 

 as mass attraction, by Copernicus. First attempt at a mathematical appli- 

 cation of the doctrine of gravitation, by Kepler. The work on the Cosmos 

 by Descartes (Traitd du Monde) nobly undertaken, did not appear until 

 long after his death, and only in fragments ; the Cosmotheoros of Huygens, 

 unworthy of the great name. Newton, and his work Philosophies Natu- 

 ralis Principia Mathematica. Endeavour towards a knowledge of the 

 universe as a Whole. Is the problem solvable of tracing back to one 

 principle all physical knowledge, from the law of gravitation to the for- 

 mative activities in the organic and animated bodies ? What has been 

 discovered does not by a long way exhaust the discoverable. The imper- 

 fectibility of empiric investigation makes the problem of explaining the 

 changeability of matter from the forces of matter an indefinite one. 



A. URANOLOGICAL PORTION of the Physical Description of the 

 Universe, pp. 29 32. 



Two sections, one of which comprises the heaven of fixed stars ; 

 the other, our solar system, p. 29. 



a. ASTROGNOS.Y ; Heaven of the fixed stars. 



I. The realms of space, and conjectures regarding that which 

 ' appears to occupy the space intervening between the heavenly 



bodies, pp. 2950. 



II. Natural and telescopic vision, pp. 51 96; Scintillation of the 

 stars, 99111; Velocity of light, pp. 111119; Results of 

 photometry, pp. 119 137. Order of the fixed stars according 

 to their luminous intensity. 



III. Number, distribution, and colour of the fixed stars, pp. 138 

 188 ; Stellar clusters (stellar swarms}, pp. 188 193 ; The 

 Milky Way interspersed with afew nebulous spots, pp. 193 203. 



IV. New stars, and stars that have vanished, pp. 204 217 ; Va- 

 riable stars, whose recurring periods have been determined, pp. 

 217 240; Variations in the intensity of the light of stars 

 whose periodicity is as yet uninvestigated, pp. 240 247. 



V. Proper motion of the fixed stars, pp. 248 252 ; Problematical 

 existence of dark cosmical bodies, pp. 252 255 ; Parallax 

 measured distances of some of the fixed stars, pp. 255 264 ; 

 Doubts as to the assumption of a central body for the whole 

 sidereal heavens, pp. 264 270. 



VI. Multiple, or double stars Their number and reciprocal dis- 

 tances. Period of revolution of two stars round a common 

 centre of gravity, pp. 271 289. 



VII. Nebulous spots. Are these only remote and very densa 

 clusters of stars ? The two Magellanic Clouds, in which crowded 



