X CONTENTS. 



117 and kii. Note 230. Distribution of the fixed stars and 

 star gaugings, p. 117 119. Star-clusters, p. 119 123. 

 Milky Way, p. 124131 and Ixiv. Ixvi. Notes, p. 245266. 



IV. Newly-appeared and Vanished Stars. Variable Stars and Va- 



riations of Light in celestial bodies of which the periodicity has 

 not yet been investigated. New stars within the last two 

 thousand years, p. 132152 and Ixvi. Ixvii. Notes 267273. 

 Vanished stars, p. 152. Periodically variable stars, p. 153 

 154 ; Colour, p. 154 ; Number, p. 155 ; subject to definite 

 laws amidst apparent irregularity ; great variations of bright- 

 ness; periods within periods, p. 156 160. Argelander's 

 table of variable stars and commentary, p. 161 171 and Ixviii. 

 Notes 274 278. Variable stars in undetermined periods 

 (T) Argus, Capella, and stars in the Great and Little Bear), 

 p. 171 176. Retrospective glance at changes which may 

 possibly have taken place in the temperature of the surface of 

 the Earth, p. 176177. 



V. Proper Motion of the Fixed Stars; Dark Cosmical Bodies; 



Parallaxes ; Doubts concerning the assumption of a Central 

 Body for the whole Sidereal Heavens : Changes modifying 

 the character of the celestial canopy, p. 178 180. Quantity 

 of proper motion, p. 180 182. Evidence in favour of the 

 probable existence of non-luminous bodies, p. 182 185. 

 Parallaxes and measurements of the distances of some of the 

 fixed stars from our solar system, p. 185 192 and Ixxi. Ixxiii. 

 Notes 308317. In double stars the aberration of light can 

 be made available for determining the parallax, p. 191 192. 

 The discovery of the proper motion of fixed stars has led to the 

 recognition of the motion of our own solar system, and even 

 to the knowledge of the direction of this motion, p. 181 and 

 193 195. Problem of the situation of the centre of gravity 

 of the whole sidereal heavens. Central Sun, p. 195 198 and 

 Ixxiii. Ixxiv. Notes, p. 327328. 



VI. Double Stars, Period of Revolution of Two Suns round a Common 



Centre of Gravity: Optically and physically double stars, 



