516 



PHYSICAL SCIENCES. 



SOLEIL. 



Soleil, M., crystals compressed by, 



189. 



Solids, conditions reducing molecular 

 particles to, 104, 105 ; distinctive 

 forms taken by matter in, 106 ; 

 velocity of sound passing through, 

 135 ; change of shape in, accom- 

 panying ringing sound, 147 ; ex- 

 pansion of, by heat, 271. 

 Solstices, the, solar motion at, affecting 

 the duration of time, 84 ; the year 

 estimated from the winter, 85 ; 

 periodical coincidence of the solar 

 perigee and apogee withu 86, 87. 



Sothaic period, the, of the Egyptians, 

 85. 



Sound, medium conveying, 129 ; its 

 propagation by undulations illus- 

 trated, 129, 130; conditions modi- 

 fying the intensity of, musical notes, 

 131 ; experiments testing the com- 

 pass of audible, 132, 133 ; media 

 modifying the velocity of, 133-137 ; 

 laws of its reflection from surfaces, 

 137, 138; undulations of, subject 

 to the laws of interference, 138, 

 139 ; laws of the foundation of 

 musical science, 140-143 ; rein- 

 forced by resonance of cavities, 150, 

 151 ; repeated vibrations required 

 to produce, 178 ; different modes of 

 action in undulations producing 

 light and, 199, 200; identical 

 nature of heat and, 280, 281 ; mea- 

 suring velocity, 290, 291. 



Sounding boards, intensifying musical 

 vibrations, 149 ; action of, in mu- 

 sical instruments, 150. 



South, Sir James, positions of stellar 

 systems measured by, 396. 



South pole, the, excess of cold at, 241. 



Sea islands, height of tides at. 



98. 



Southern Ocean, rise of the tidal wave 

 in, 93 ; velocity of the wave, 94. 



Spain, meteoric showers off the coast 

 of, 421. 



Specific heat defined, 275. 



Spectra of gases and flames, their 

 characteristic peculiarities, 163, 

 164 ; three superposed, of the pure 

 white sunbeam, 222. 



Spectrum, the solar, decomposed into 

 seven colours, 159 ; colours of, modi- 

 fied by thickness of the medium 

 absorbing, 160 ; decomposed into 

 three colours, 161 ; ray less lines 

 in, 162 ; observations and experi- 

 ments on rayless lines, 163,164; 

 experiment of fluorescent light, 197 ; 

 obtained independently of prismatic 

 retraction, 201 ; energetic action of, 

 on matter, 203 ; photographic co- 

 loured images of, 208-210 ; analysis, 

 properties of, experiments, 211-219; 

 complex nature of, 222 ; produced 

 from diffracted light, 223. 



of an electric spark, 289. 



of the Voltaic arc, 303. 



Spheres,mode of attraction in hollow and 

 solid, 4 ; planets partaking the nature 

 of, 7 ; impulses regulating rotations, 

 ib. ; conditions procuring the figure 

 of, 44 ; formula finding the density, 

 56 ; force giving the form of, 106 ; 

 power of retaining electricity, 288. 

 Spherical form, the result of cohesion, 



106. 



Spheroids, influencing attraction dif- 

 ferently from spheres, 4 ; force dis- 

 turbing attraction in, 27 ; com- 

 pression of the terrestrial and of 

 Jupiter's, computed, 38, 39 ; of 

 elliptical strata, quantities invari- 

 able in, 46 ; of the sun, 65 ; effect 

 produced by the attraction of an 

 external body on, 79 ; power of 

 retaining electricity, 288. 

 Spiral nebula, 409, 410. 

 Spots on the sun's surface, periods of 

 their vicissitudes, 224 ; amount of 

 heat varying with, 225. 

 Spring tides, 96-99. 

 Springs, hot, rising in mines, 229 ; 

 mean heat of the earth determined 

 from, 238. 

 Standards of weights and measures, 



whence derived, 89, 90. 

 Stars, fixed, the, the solar system pro- 

 bably not independent of, 24 ; ve- 

 locity of light deduced from aberra- 

 tion of, 31; vast distances of, 54 ; 

 precession affecting their longi- 

 tudes, 80 ; computations of their 



