452 



the fixed stars, ib. He misses a 

 star, 363. His account of the star 

 Algol, 364. Determines the ellip- 

 tical motions of binary systems, 

 367. Determines the orbit of y 

 Virginis, ib. Adds to the cata- 

 logue of double stars, 368. On 

 the color of the stars, 374. On 

 clusters of stars, ib. On the ne- 

 bula;, 376 et seq. 



Herschel, Miss Caroline, her obser- 

 vations of Encke's comet, 345. 

 Her catalogue of nebulae, 376. 



Hevelius first noticed the contrac- 

 tion of comets in approaching the 

 eun, 356. Thought he saw the 

 phasesof a comet, 357. Mentions 

 a variable star, 364. His obser- 

 vations of Halley's comet, 343. 



Hipparchus discovers precession, 75. 

 His catalogue of stars, 363. 



Homogeneous light, 154. 



spheroid, its rotation, 44. 



Horizontal refraction, 39. Note 113. 



- parallax of the moon, 51. 



Horoscope, 84. 



Hit m bold t, Baron, his observations 

 on the Gulf-stream, 04. Effects 

 .of the rarity of the air on, 114. 

 His observations on the transmis- 

 sion of sound, 189. On the tem- 

 perature of mines, 242. On the 

 distribution of heat, 254. His bo- 

 tanical observations, 266. On the 

 distribution of plants, 267. On 

 the Gulf-weed, 268. His observa- 

 tions on terrestrial magnetism, 

 330. 



Hurricanes, laws of, 119. 



Huygens, his undulatory theory of 

 light, 163. 



Hyperbola, 12. Note 22. 



I. 



Ibn Junis, his observations, 85. 



Ice, its double refraction, 177. 



useful for polarizing light, 183. 



impermeable by Voltaic elec- 

 tricity, 298. 



Icebergs drifted from the poles, 95. 



collision of, a cause of light, 



280. 



Iceland spar, a carbonate of lime, 

 its form, 175. Note 166. 



, a doubly refracting substance, 

 176. Note 200. 



useful as an analyzing plate, 

 181 



Iceland spar a negative crystal, 177. 



Image from a crystal with one op- 

 tic axis, 183. Note 207. 



from a crystal with two optic 



axes, 182. Note 208. 



Impetus, a force proportional to the 

 mass and the square of the ve- 

 locity of the striking body con- 

 jointly, 131. 



Imponderable agents, 336. 



Inactive lines in photographic spec- 

 trum, 204. 



Inclination of planetary orbits, 9. 

 Note 53. 



variation of, 18. Note 72. 



Indians, the lunar tables of, 83. 



Inequalities. See Perturbations. 



Insects, the distribution of, 270. 



Intensity of light, 164. 



of sound, 124, 130. 



of gravitation, 4. 



Interference of waves, 92. Note 147. 



of tides at Batsha in Tonquin, 



93. 



of sound, 133. 



of light, 161, 187. Notes 193, 



211. 



Internal heat of the earth, 67, 242 

 et seq. 



structure of the earth, 74. 



structure of Jupiter, 28, 57. 



structure of Saturn and Mars, 



57. 



Invariable plane of the solar system, 

 22. Note 80. 

 , position of, 22. Note 81. 



of the universe, 23. 



i Inverse square of distance, 5. Note 

 I 23. 



cube of distance, 55. Note ] 33. 



Iron, its magnetic properties, 305, 

 327. 



Isogeothermal lines, 260. 



Isomorphism, 106. 



Isothermal lines, 259. 



Ivory, Mr., his determination of the 

 form of the terrestrial spheroid, 

 43, 47. His formuhe for baro- 

 metrical measurements, 113. On 

 the distribution of the electric flu- 

 id, 276. 



Jews used the week of seven days, 



80. 



Jovial System, the mass of, 55. 

 Julian Calendar, 80. 

 Jupiter, the compression of, 62. 



