capability of producing fluorescence, 196 capability of, in rays, affect- ing their chemical action, 209- 212; effect of, on the lunar atmo- sphere, 226; influence of, transmission of heat, 258; of rays of heat, 261-264; heat polarized by, 266. Refrangibility, substances diminishing, of light, 196; affecting the che- mical action of rays, 209-212; affecting radiation of heat, 257; affecting transmission of radiant heat, 261-263.
Reich, Professor, temperature of mines observed by, 228; mean increase calculated by, 230. Reptiles, distribution of distinct species of, 254.
Repulsion of electricities, 283; expe-
riments determining the laws of electrical, 286, 287; modes of, in static and in Voltaic electricity, 317; developing comets' tails, 375- 377.
Resistance, a cause of accelerated motion, 367.
Retina, the, action of, in receiving im- pressions, 166; comparative sen- sibility of its fibres to light,
Retrograde motion of comets, 359, 368, 373, 379.
Rhodiola rosea, identical species of, found in Tartary and in Scotland, 251.
Rhombohedrons of carbonate of lime, 109.
Richman, Professor, killed by light- ning, 293.
Richter, variation in length of the pendulum observed by, 51. Rings of Saturn, 66-68; Saturn's, diamagnetic, 347; luminous, sur- rounding comets, 374, 375; sur- rounding Donati's, 379. Ritchie, Professor, electrical experi- ments of, 314.
Ritter, M., chemical properties of the
solar spectrum observed by, 203; oxydizing effect of red rays, 209. Rive, M. Auguste de la, rate of in-
crease of temperature in wells ob- served by, 230.
Rivers, curvature of the land proved by, 46; influence of, on the earth's rotation, 71; rising of tides in, 98; effect of, in cooling the atmo- sphere, 243.
Roget, Dr., phenomena of electro- magnetism explained by, 313. Rome, observations on lunar moun-
tains made at, 70; era fixed at, 85; comet discovered from, 370.
Ross, Sir James, stratum in the ocean discovered by, 101; depressure of the barometer observed by, 120; volcanic region discovered, 232. Rosse, Lord, nebulæ resolved by his telescope, 407, 408; spiral nebula, 409, 410; annular nebulæ dis- covered by, 410; nebulous star, 411; planetary nebulæ, 412; ne- bulæ resolved by, 415.
Rotation affecting winds, 122-127; of
winds, 124, 125; of hurricanes, 125, 126; produced by the Voltaic current acting on iron, 305; of stratifications of electrical light, 307; caused by electricity, 313, 314; of light caused by an electric current, 319; of magnets pro- ducing electricity, 330-332; changes produced in comets by, 376.
Rotations of the solar system, 7; of the sun, 65; of the planets, 66; of satel- lites, 68; of Jupiter's satellites, 70; of the earth, a measure of time, 71; influence of temperature on, 72; axis of, invariable, 76, 77. Rotatory motion, form indicating, 65; of Donati's comet, 379. Roux, M. le, observations on magnetic action in crystals, 350. Rudberg, M., refrangibility of sub-
stances ascertained by, 201, 202. Ruhmkorff, M., improvements on his
electro-inductive apparatus, 328. Russell, Scott, Mr., velocity of the
tidal wave estimated by, 95. Russia, arc of the meridian measured in, 48; climates of, 244.
SABINE, General, variations in the magnetic elements investigated by, 343, 344.
Sagittarius, comet traversing constellation of, 379; the Milky Way in, 386; nebula, 414. Sahara, the, causing monsoons, 124. desert, extent, influence of, on the atmosphere, 243.
Salt, Mr., papyrus sent from Egypt by, 89.
Sand, tubes in, formed by lightning, 293.
Sandy deserts influencing temperature, 243.
Sandwich Land, excess of cold in, over
corresponding latitudes, 241. Sargassa, or grassy sea, found in the Atlantic, 253.
Satellites, intensified action of attrac-
tion upon, 7; intimate union of, with their primaries, 26; excep- tions to a general law of the solar system, 65, note; rotations equal to the times of their revolutions, 68; comet passing through, 69.
-, Jupiter's, proportion of their mass to that of their primary, 27; disturbing force of attraction affect- ing their orbits, 28; periodic and secular inequalities, 28, 29; eclipses, 30; rotation, 70; passage of a comet through, 359; comet nearly approaching, 370.
of Saturn, 32; of Uranus and Neptune, 33.
mode of computing their masses, 55; comparative density of, 58. of Neptune, 63.
of the earth, shooting stars,
Saturn, unequally occurring compen- sations of disturbance in its motions, 15; disturbing influence of, on Jupiter, excentricity of its orbit compared with Jupiter's, 17; re- tarding the revolution of Jupiter's nodes, 19; invariable plane passing between Jupiter and, 24; observa- tions on the mean motions of Ju- piter and, 25, 26; eclipse of, 42; internal structure, 58; astronomical
tables of, 60; period of his year, 66; the rings of, described, 66-68; his ring probably diamagnetic, 347; action of, on Halley's comet, 362, 363; comets having their perihelia in his orbit, 381.
Saurian reptiles, distinct tribes of, 254.
Saussure, M., temperature of mines
observed by, 228, 229; lichen dis- covered by, 249. Savart, M., his researches and experi- ments in acoustics, 132, 133; ex- periments on vibrations of glass rulers, 145-147; experiments show- ing sympathetic undulations, 148, 149; discoveries on the nature of voice, 152.
Savary, M., orbital elements of a double star determined by, 396; his mode of ascertaining the actual distances of fixed stars, 402, 403.
Scheele, M., chemical changes effected by the solar spectrum observed by, 203. Schroëter, height of planetary atmo-
spheres calculated by, 226. Schwabe, M., periodic variation in the
solar spots observed by, 344. Science, its value regarded as the pursuit of truth, 1; errors of the senses corrected by, 32; evidence of its antiquity, 87.
Sciences, mutual relations of forces proving the connexion between, 319-321; analysis proving the whole circle of, kin, 427, 428. Scoresby, Captain, phenomenon occa- sioned by refraction observed by,
Scorpio, vacant patch of the Milky Way in, 386; position of, 390; a double star in, 395; nebula in, 414.
Scotland, progress of the tidal wave round, 94.
Sea, the, inappreciable influence of,
on the direction of gravity, 77; mean height of snow-line above the level of, 241; comparative extent of, 242.
Seasons, conditions determining the duration of, 74; cause of their un- equal periods, 87; theory of the tropical dry and rainy, 123. Seaweeds, photographic impressions of, 205, 206; luxuriance, deep colours of, 253. Secchi, Professor, mountains of the moon observed by, 70; photo- graphic image of the moon obtained, 214; temperatures of the sun's surface estimated, 225; experi- ments of, in photographing the moon and Jupiter, 226, 227. Secular inequalities of planets, 13,
14; means of discovering, 24, 25; effect of, on the mean motion of the moon, 36, 37.
variations in mean values of the magnetic elements, 343. Seebeck, point of maximum heat in solar spectrum fixed by, 263; dis- covery of, 264; relations of heat to electricity discovered by, 332, 333. Seed-lobes, proportion in the distri- bution of plants having one or two, 252.
Seleniate of zinc, crystals of, 107. Senarmont, M., experiments of, in ex- pansion of crystals, 273. Senses, necessarily inaccurate testi- mony of the, 281.
September, times coinciding in, 84. Serpentarius, star in, vanishing, 392. Shell-fish, their mode of clinging to rocks, 117.
Shield, the, clusters of the Milky Way between Ophiuchus and, 387. Shooting stars, phenomena of, de- scribed, 421, 422; theories of, 423.
Siberia, Eastern, depression of the barometer observed in, 120. Sidereal times, mean, periods of, 83; measurement of apparent, ib. Sigma Eridani, period of revolution in, 400.
Silesia, fulgorites from, 293.
Silver iodized, its sensitiveness to im- pressions, 221.
Sirius, the Egyptian year estimated from, 85; comet's tail extending
from the Hare to, 373; rank of, 384; comparative magnitude, 385; parallax, 389; cause of his irre- gular motion, 392; change in colour, 401; light, 402; extent of surface, 404.
Smyth, Admiral, his measurement of Etna compared with Sir John Her- schel's, 120; eclipse of a double star observed by, 397; its periodic time determined, 398.
-, Piazzi, heat of the moon felt by, 227.
Snow, cause of perpetual, on summits of alpine chains, 119; causes modi- fying the height of the line of per- petual, 241; protecting vegetation, 249; radiation of heat by, 257. Soda, sulphate of, change of form in its crystals, 107; crystals of the neutral phosphate and the arseniate of, 109.
Soil, the, dependence of temperature on the nature of its products, 243. Solar gravitation, 424, 425.
magnetism, its connexion with terrestrial, 344.
spectrum, cause of the point of maximum heat varying in, 263,264.
system, the, gravitation of the bodies composing, 5; conditions securing the stability of, 11, 12; proof of its stability, 20; equi- librium of, underanged by the ethereal medium, 22; invariable plane, forming the equator of, 23, 24; question of its revolution round a common centre, 24; pro- perties of its medium, 32; masses of bodies composing, 55, 56; their diameters, 56; uniform direction of rotation in, 65; comparative apparent importance of, in creation, - 226; probably magnetic through- out, 346; comets forming part of, 365; possible ultimate destruction of, 372; computations of comets revolving within, 381, 382; paths described by heavenly bodies in, 382, 383; position of, relatively to the Milky Way, 385; direction of its motion, 405,
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 with, 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; rayless lines in, 162; observations and experi- ments on rayless lines, 163, 164; experiment of fluorescent light, 197; obtained independently of prismatic refraction, 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
positions furnishing historical data, 88, 89; made visible by refraction, 154; peculiar law of light demon- strated by the aberration of, 202; magnitude of the solar system seen from, 226; numbers, classification of, 384; positions, 385; the Milky Way, 385-387; parallaxes and distances of, 387-389; variable, 390-395; missing, 395; systems of multiple, classified, ib.; binary, 395-406 (see Double stars); ne- bulous, 406-419 (see Nebula); seemingly innumerable, 420; me- teors, 420-423.
Static electricity, 282: see Elec- tricity.
Steam, formation of, 269; force con- verting liquids into, 277; measure of its elasticity, 278; question of its being superseded by electricity, 328. Steel, paramagnetism induced in, 336; conditions of magnetic power re- maining permanently in, 337, 338; its elasticity affected by magnetism, 352.
Stephenson, George, quotation from, 279-280.
Stokes, Professor, remarks of, on gra- dation of colours, 161; experiments on fluorescence of light, 197; his decision with regard to vibrations of polarised light, 223.
Storms, magnetic, 344; varying with latitude, 345, 346.
Strata of the earth, position and com- parative density of, 77. Stratifications, experiments showing, in electric light, 306, 307. Struve, M., measurement by, 48; his observations on Saturn's rings, 68; occultation by a comet observed by, 364; comet's nucleus described, ib.; distance of a fixed star measured by, 388, 389; catalogue of double stars, 396; remarks on colour and light of double stars, 401; sun's motion proved by, 405.
Stutgardt, natural hot springs used in manufactories near, 231. Submarine telegraph, 325-327.
Sulphate of magnesia, its crystals boiled in alcohol, 108.
of nickel, effect of exposure to the sun, on its crystals, 107. of soda, its crystals, 107. of zinc, experiment on its crys- tals, 108.
Sulphuretted hydrogen gas, its con- stituent parts, 111.
Sumbawa, volcanic eruption of, 233. Summer, mean temperature of, vary- ing in the same latitude, 246, 247; atmospheric electricity in, 291. Sun, the, law regulating his attraction of heavenly bodies, 5; effect of his attraction on planetary orbits, mean distance of planets from, 8; im- portance of his magnitude in the solar system, 12; disturbances in the relative positions of planets and, 14; force modifying his intensity of attraction, 16; resistance offered by, to the power of disturbing forces, 20; periods of conjunc- tions of Jupiter, Saturn, and, 25; influence of, on lunar motions, 34, 35; action of the planets re- flected by, 37; eclipses of, 40, 41; supposed constitution of, 41; his atmosphere, 42; mode of finding his parallax, 52, 53; mean distance from the earth, 53; mass of, 55; diameter, 56; comparative density, attractive force, 56, 57; astrono- mical tables of, 63; deductions from his rotation about an axis, period of, 65; attraction of, pro- ducing a precession of the equinoxes, 79, 81; returns of, a measure of time, 83-85; divisions of time, de- pendent on revolutions of the major axis of his orbit, 86, 87; action on tides, 92, 97; disturbing the equi- librium of the atmosphere, 121; dry and rainy seasons regulated by, 123; cause of decreased light and heat in horizontal rays, 157, 158; distance of, falsely estimated, 158; light polarized by, 195; indications of an absorptive atmosphere sur- rounding, 212, 213; his diameter, 224; appearance of, through his
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