Till GENERAL SUMMARY 



15 18. Radiation of heat by the stars, p. 42, note 26. Temperature 

 of space, pp. 44 47. Limited transparency? p. 46. Regularly de- 

 creased period of revolution of the Comet of Encke, p. 47. Limitation 

 of the atmosphere ? p. 49. 



II. Natural and telescopic vision: Very different sources of light 

 present similar relations of refraction, p. 54. Different velocities of the 

 light of ignited solid bodies and that of frictional electricity, p. 56. 

 Position of the Wollastonian lines, p. 56. Influence of tubes, p. 53. 

 Optical means of distinguishing between direct and reflected light, and the 

 importance of the means to physical astronomy, p. 56. Limits of 

 ordinary vision, p. 60. Imperfection of the organ of vision ; false 

 diameter of the stars, p. 66. Influence of the form of an object upon 

 the minimum visual angle in experiments as to visibility; necessity of a 

 difference of luminous intensity of ^ ; visibility of distant objects, positively 

 and negatively, pp. 61 72. On the visibility of stars by day with the 

 naked eye from wells or upon lofty mountains, p. 72. A feeble light 

 by the side of a stronger, p. 61, note 15. Extending ray and star tails, 

 p. 65. On the visibility of the satellites of Jupiter by the naked eye, 

 p. 64. Undulation of the stars, p. 77. Commencement of telescopic 

 vision; application to measurement, pp. 78 81. Refractors of great 

 length, p. 81. Reflectors, p. 82. Day observations ; how strong mag- 

 nifying powers facilitate the finding of the stars by day, p. 87. Ex- 

 planation of the sparkling and scintillation of the stars, p. 96. Velocity 

 of light, pp. 105 118. Order of magnitude of the stars; photometric 

 relations and methods of measurement, pp. 119 132. Cyanometer, 

 p. 129. Photometric order of the fixed stars, pp. 132137. 



III. Number, distribution, and colour of the fixed stars; Stellar 

 clusters and the Milky Way: States of the sky which hinder or favour 

 the detection of stars, p. 138. Number of the stars; how many may be 

 seen with the naked eye, p. 140. How many have been inserted in 

 stellar charts with determinations of position, p. 145. Conjectural 

 estimation of the number of stars which can be visible in the entire 

 heavens with our present powers of penetrating space, p. 141. Con- 

 templative astrognosy of uncivilized people, p. 147. The Grecian sphere, 

 p. 159. The crystal sky, p. 164. False diameter of the fixed stars in 

 telescopes, p. 174. Smallest objects in the heavens which have yet been 

 seen, p. 175. Difference of colours in the stars, and the changes which 

 have taken place in the colours since antiquity, p. 175. Sirius (Sot/iis), 

 p. 178. The four royal stars, p. 184. Gradual acquaintance with the 

 Southern heaven, p. 185. Distribution of the fixed stars, laws of relative 

 accumulation, gauging, p. 187. Clusters and swarms of stars, p. 189. 

 The Milky Way, p. 193. 



IV. Stars that have newly appeared and disappeared ; variable stars 

 and changes in the intensity of their light whose periodicity has not been 

 investigated: New stars in the last 2,000 years, p. 204 Periodically 

 changeable stars: Historical particulars, p. 203. Colour, p. 24. 



