Vlll CONTENTS. 



MORE DETAILED ANALYSIS OF THE DIFFERENT SECTIONS 

 OF THE ASTRONOMICAL PORTION OF THE COSMOS. 



a. ASTROGNOSY. 



I. Cosmical Space : Only separate parts of it accessible to measure- 

 ment, p. 31. Resisting medium, celestial air, cosmical sether, 

 p. 83 and x. Notes 6063. Radiation of heat from stars, 

 p. 36 and xii. Notes 71 and 72. Temperature of space, 

 p. 37 39 and xii. xiii. Notes 7477- Limited transparency ? 

 p. 39 40. Regularly diminished period of revolution of 

 Encke's comet, p. 40 41 and xiii. Note 83. Limit of the 

 atmosphere? p. 42. 



II. Natural and Telescopic Vision : Effect of tubes, p. 4445 and xv. 

 Note 94. Very different sources of light shew similar relations 

 of refraction, p. 45. Difference in the velocity of light pro- 

 ceeding from glowing solid bodies and light of friction- 

 electricity, p. 46, 7477, and xxxiv. xxxv. Notes 145149. 

 Position of Wollaston's lines, p. 46. Optical means of distin- 

 guishing between direct and reflected light, and importance of 

 these means for physical astronomy, p. 46 and xvi. Notes 

 98 102. Limits to ordinary visual power, p. 47. Imper- 

 fection of the visual organ, factitious diameters of stars, 

 p. 4950 and xviii. xxi. Notes 104106. Influence of the 

 form of objects on the smallest angle at which they can be seen ; 

 necessity of a difference of one-sixtieth between the intensity 

 of light in the object and its background, p. xxvii. Distant 

 objects seen in a positive or negative manner, p. 49 53. On 

 stars being seen in the day-time by the naked eye from the 

 bottom of wells or mines, or on the summits of high mountains, 

 p. 5355 and xxii. Note 110. A fainter light by the side of 



