Contents xix 



PAGE 



148. The Rudolphine Tables 194 



149. Work under Wallenstein : death .... 195 



150. Minor discoveries : speculations on gravity . . 195 



151. Estimate of Kepler's work and intellectual character 197 



CHAPTER VIII. 

 FROM GALILEI TO NEWTON (FROM ABOUT 1638 A.D. TO 



ABOUT 1687 A.D.), 152-163 198-209 



152. The general character of astronomical progress 



during the period 198 



153. Schemer's observations oifaculae on the sun. Hevel\ 

 his Selenographia and his writings on comets : 

 his star catalogue. Riccioli's New Almagest . 198 



154. Planetary observations: Huygens's discovery of a 



satellite of Saturn and of its ring . . 199 



155. Gascoigne's and Auzoufs invention of the micro- 

 meter : PicarcCs telescopic " sights " . . . 202 



156. Horrocks : extension of Kepler's theory to the 



moon: observation of a transit of Venus . . 202 



I 57~8. Huygens's rediscovery of the pendulum clock : 



his theory of circular motion .... 203 



159. Measurements of the earth by Snell, Norwood, and 



Picard 204 



1 60. The Paris Observatory : Domenico Cassini: his 

 discoveries of four.new satellites of Saturn : his 

 other work ........ 204 



161. Richer s expedition to Cayenne : pendulum observa- 

 tions : observations of Mars in opposition : hori- 

 zontal parallax : annual or stellar parallax . . 205 



162. Roemer and the velocity of light .... 208 



$ 161. Descartes . , 208 



CHAPTER IX. 



UNIVERSAL GRAVITATION (FROM 1643 A.D. TO 1727 A.D.), 



164-195 210-246 



164. Division of Newton's life into three periods . . 2IO 



165. Early life, 1643 to 1665 210 



166. Great productive period, 1665-87 . . . .211 



