stars of 1st magnitude, 137 ; of 

 the variable stars, by Argelander, 

 232, and explanatory remarks, 

 233240 ; of ascertained paral- 

 laxes, 262 ; of the elements of 

 the orbits of double stars, 289. 



Telescope, the principle of, known 

 to the Arabs, and probably to the 

 Greeks and Romans, 53; disco- 

 veries by its means, 78 ; succes- 

 sive improvements of the, 80 ; 

 enormous focal length of some, 

 81 ; Lord Rosse's, 85 ; Bacon's 

 comparison of, to discovery ships, 

 175 ; penetrating power of the, 

 196. 



Telesio, Bernardino, of Cosenza, his 

 views of the phenomena of inert 

 matter, 16. 



Temperature, low, of celestial space, 

 42 ; uncertainty of results yet 

 obtained, 43 ; its influence on the 

 climate of the earth, 45. 



Temporary stars, list of, 209 ; notes 

 to, 210217. 



Ternary stars, 286. 



Timur Ulugh Beig, improvements 

 in practical astronomy in the 

 time of, 121. 



Translation in space of the whole 

 solar system, 265 ; first hinted 

 by Bradley, 265 ; verified by 

 actual observation by William 

 Herschel, 266 ; Argelander, 

 Struve, and Gauss's views, 266. 



Trapezium in the great nebula of 

 Orion, investigated by Sir William 

 Herschel, 276. 



Tycho Brahe, his vivid description 

 of the appearance of a new star, 

 205 ; his theory of the formation 

 of such, 208. 



" "Ultimate mechanical cause" of all 



motion., unknown, 27. 

 Undulation of the stars, 75. 

 Undulations of rays of light, various 



lengths of, 112. 

 Unity of nature distinctly taught by 



Aristotle, 11 14. 



Uranological and telluric domain of 

 the Cosmos, 29. 



Uranus observed as a star by Flam- 

 stead and others, 153. 



Vanished stars, 221 ; statements 

 about such to be received with 

 great caution, 221. 



Variable brightness of multiple and 

 double stars, 285. 



Variable stars, 218 ; mostly of a red 

 colour, 224 ; irregularity of their 

 periods, 226; table of, 232. 



Velocity of light, 105 ; methods of 

 determining, 106 ; applied to the 

 determination of the parallax, 265. 



Visibility of objects, 70 ; how modi- 

 fied, 71. 



Vision, natural and telescopic, 51 ; 

 average natural, 60 ; remarkable 

 instances of acute natural, 66, 70. 



Wheatstone's experiments with re- 

 volving mirrors, 56 ; velocity of 

 electrical light determined by, 

 114. 



White Ox, name given to the nebula 

 now known as one of the Magel- 

 lanic clouds, 122. 



Wollaston's photometric researches, 

 127. 



Wright, of Durham, his view of the 

 origin of the form of the Milky 

 Way, 201. 



Yggdrasil, the world-tree of the 

 Edda-Songs, 4, 5. 



Zodiac, period of its introduction 

 into the Greek sphere, 160; its 

 origin among the Chaldeans, 161 ; 

 the Greeks borrowed from them 

 only the idea of the division, and 

 filled its signs with their own 

 catasterisms, 161; great antiquity 

 of the Indian very doubtful, 163. 



Zodiacal light, Sir John Herschel on 

 the, 48. 



