plane of the ecliptic, 18, 19; stable and unstable in form, 21, 22; influence of the ethereal medium on, 22; principle facilitating ob- servations on secular inequalities, 23, 24; revolutions of Saturn compared with Jupiter, 25; peri- odic inequality increased by secular variations in their elements, 26; comets revolving in, 381, 382; cause of diversity in form of,
Orbits of satellites, forms of Jupiter's, 27; their inclinations, 28; in- clinations of Saturn's, 32; positions of Uranus's, 33; forms of data in computing a planet's place in the heavens, 59.
Orinoco, the cataracts of the, heard
by day and by night, 135; area occupied by forests on, 243. Orion, the Milky Way between An- tinous and, 385, 386; position of, 390; variable star in, 393, 394; multiple system in, 395; nebula in, 408.
Oersted, Professor, discovery of, sug- gesting the theory of electro-mag- netism, 312; science founding the reputation of, 316. Oscillations, wide-spreading, produced by gravitation, 2; mechanical principle affecting small, 11; of the sines and cosines of circular arcs, 20; invariable plane whence they may be estimated, 24; of the pendulum retarded, 32; of the pendulum, experiments founded on, 50, 51; experiments testing the earth's density, 57; a measure of time, 83; produced by tides, 95, 96; instruments measuring atmo- spheric, 113; barometer affected by periodic atmospheric, 120, 122; of ears of corn, 129, 130; pro- ducing musical notes, 140-142; instances of forced sympathetic, 148; causing vicissitudes in cli- mates, 247; of the pendulum, dis- turbed by effects of temperature, 272; measuring variation of elec- trical intensity, 287.
Otaheite, transit of Venus observed at, 53.
Otto, M., motions of the heavenly bodies observed by, 405. Oxidation of metals, electricity de- veloped by, 298; by the Voltaic discharge on polished silver, 305. Oxides decomposed by electricity, 307; alkalies resolved into metal- lic, 307.
Oxygen, in crystals, 109; proportion of, in water and carbonic oxide, 111; in the atmosphere, 117; chemical combination with, evolving light and heat, 270; action of electricity on, 284; electricity afforded by combination of metals with, 298; spectrum from, 303; separated from water by electricity, 307; paramagnetic, 344.
Ozone, produced by electricity, 284.
PACIFIC Ocean, mean depth of, 77;
course of tidal waves down, 93; mean depth of, 96; currents, 100. Paderborn, fulgorites from, 293. Pallas, inclination of its orbit to the
ecliptic, 10; diameter of, 21; astro- nomical tables, 63; ellipticity of its orbit compared with the terres- trial, 74; height of its atmosphere, 226; comet revolving between the orbits of Mercury and, 367. Pan's pipes, vibrations in the air pass- ing over, 142.
Parabolic motion, ratio of forces pro- curing, 382.
Parallax of the sun, circumstance favourable to its correction, 21.
of an object defined, 43.
definition, mode of ascertaining, 52; distances computed from, 52- 54; calculation from the moon's horizontal, 55.
of fixed stars, 387-390. of meteors, 421, 422. Paramagnetic substances, 335, 336. Paramagnetism defined, 335; sub- stances it is resident in, 336; modes of imparting, ib.; a dual power, ib. ; imparted by induction, 337; law of its intensity, 338; a property of
oxygen, 344; in antithesis to dia- magnetism, 347; neutral substances obtained by combinations of dia- magnetism and, ib.; Dr. Tyndall's experiments on polarity of, 348; dependent on arrangement of mole- cules, 350, 351; affected by com- pression, 351; truth establishing its identity with diamagnetism, 356, 357. Parathermic rays, analyzed by Sir John Herschel, 217-219. Paris, variation in length of the pen- dulum at, 51; mean annual tem- perature, 228; temperature of an Artesian well in, 230. Paths of comets, 359, 360; secrets
disclosed by their excentricities, 365. Parry, Sir Edward, turned back by the Polar current, 101; mean tem- perature calculated from observa- tions of, 245; thermometer at Mel- ville Island marked by, 247. Pauxis, the Straits of, ebb and flow of the sea in, 98.
Peel, Sir William, thunderstorm ex- perienced by, 293, 294.
Pegasus, nebulous region of, 417. Pendulum, the, principle equalizing its oscillations, 50; the earth's figure calculated by, 50, 51; ex- periments ascertaining the earth's density, 57; isochronous, a measure of time, 83; a standard of the mea- sure of extension, 89; the, a con- necting link between time and force, 94; inventions to neutralise the effects of temperature, 272. Penumbra, in lunar eclipse, breadth of space occupied by, 40. Perigee, of the lunar orbit, period of its revolution, 37, 38; cause of its rapid motion, 55.
solar, periods of its coincidence with the equinoxes, 86. Perihelion of a planet's path defined, 16.
of the earth's orbit, its position regulating the length of seasons, 74. Periodic inequalities of planets, 13, 14; law from which they are de- duced, 24, 25; of Jupiter's satel- lites, 28, 29; lunar, 35.
PHOSPHORESCENCE.
Perkins, Mr., experiments of, testing the laws of compression, 78. Peron, M., specific diversity of marine animals asserted by, 254. Perpendicular force, the source of pe- riodic inequalities, 15; effects pro- duced by, 18. Perpetual motion, invariable propor- tion between heat and force pre- cluding, 279.
Perseus, variable star in, 390, 391. Peters, Mr., comet discovered by, 370; parallax of a Lyræ, 388, 389; dis- tances of fixed stars calculated, 389; his theory of Sirius' irregular mo- tions, 392; sun's motion proved by, 405.
Petit, M., observations of, on meteoric satellites, 423.
Peru, arcs of the meridian measured in, 48.
Phases of the moon, regulating returns of eclipses, 39.
Phenomena, of effects of light in eclipses, 41, 42; applied to com- puting longitudes, 43; caused by tidal oscillation, 96; from force of cohesion, 106, 107; of capillary attraction, 115; produced by re- fraction and reflection, 155-157; by polarization of light, 186-190; ex- hibited in fluorescence of light, 196, 197; resulting from interaction of rays and molecules, analogous to effects of photography, 219-222; phosphorescent, 295, 296; of gal- vanism, 310; of magnetism, 335, 345-348; magnecrystallic, 349, 350; exhibited by comets, 363, 364, 369, 370, 372-376; by the Milky Way, 385-387; by variable stars, 390-393; by double stars, 397-401; by nebula, 409-415, 417-419; by meteoric showers, 421, 422. Phosphorescence, rays of the solar spectrum exciting, 216; cause of, in the solar spectrum, 217; excited by electricity, 294; fish possessing the property of, 295; the glow discharge, 295, 296; experiments investigating the nature of, 296.
Photo-galvanic engraving, 309. Photography, first suggestions, 203; discoveries and improvements in, 204-207; conditions affecting the chemical properties of rays pro- ducing, 207, 208; images of the solar spectrum obtained by, 208- 210; coloured copy of an engraving, 211; phenomena in, suggesting an absorptive action in the solar at- mosphere, 212, 213; chemical energy producing, distinct from light and heat, 214; experiments by means of, testing the properties of rays, 218, 219; experiments on action of light, heat, electricity, producing results analogous to ef- fects of, 219-223.
Photosphere, the, of the sun described, 224.
Physical Sciences, the most extensive example of their connection, mode of its operation, 1.
Pi Herculis, direction of solar motion with regard to, 406. Pisces, nebulous region of, 417. Planetary motion, representation of, 14.
nebulæ, 409; appearance of,
Planets, paths round the sun described by, 5; law determining their revo- lutions, ib.; forces adjusting their forms, 6; their motions in elliptical orbits, mean distance from the sun, 8; mode of obtaining the place of, in their orbits, 9; computations giving the place of, in space, 10; disturbances from reciprocal attraction affecting, compensations, 13-19; telescopic, 20, 21; pertur- bations in the mean motions of, 25, 26; influence of, on lunar motions, 36; eclipses and conjunctions of, 42; formula finding their masses, 55; their diameters, 56; mass of the telescopic, compared with the moon, ib.; comparative density, 58; me- thod of computing their places, 58- 64; discovery of, 61-63; exploded theory touching telescopic, 63; pe- riods of their rotations, 66; va-
riation and position of the plane of the ecliptic produced by, 79; its effect on the equinoctial points, 80; climates of, 225, 226; probably magnets, 346; constant velocity of their mean motions, 366. Plants, distribution of known species over the globe, 249, 250. Plates, vibrating, experiments by means of, 144-146.
Plateau, M., experiments of, on colour, 165, 166.
Platina, incandescent, used as a source of heat, 260. Platinum, experiment producing spon-
taneous combustion of, 112, 113. Playfair, Professor, quoted in reference to La Grange's discovery, 23. Pleiades, the, nebulous stars, 415. Plücker, Professor, discoveries of, in the action of magnetism in crystals,
vegetation, contrasted with tro- pical, 248. Polarity, produced by electricity, 282; of magnets defined, 336; induced in iron, 337; its antithetical mani- festations of, 339; invariably dual, 341; of diamagnetic substances, 347, 348. Polarization of light, definition of, 179; refracted by various sub- stances, 180-183; by reflection, 184; angles of, 185; phenomena exhibited by transmission through analyzing media, 186-188; circular, 189-191; theory of circular and elliptical, 192, 193; substances pro- ducing, 193, 194; theory of co-
POLARIZATION. loured images formed by, 194; ac- cidental, 195; discovery of, ib.; degraded light incapable of, 198; communicating electricity, 220; plane of motion of vibrations in, 223.
Polarization of heat, first attempts, 264; successful experiments, 265- 267.
of electricity by induction,
experiment showing the action of magnetism on, 319; affected by mechanical compression, 352. Poldice mine, the, temperature of the water pumped from, 229. Poles, the, cause of the flattening of a spheroidal mass at, 6; diameter of Jupiter at, 27; experiment deter- mining the increase of gravitation towards, 49, 50; the, drifting of ice from, 100, 101; of maximum cold, centres of the isothermal lines, 245, 246; nature of magnetic force distinguished by, 332; four terres- trial, of maximum magnetic force, two magnetic, 343.
Pollux, an optically double star, 401. Port Bowen Harbour, transmission of sound across, when frozen, 136. Positive electricity, defined, 282; mode of exciting, 283.
impressions in photography, 204. Pouillet, M., his estimate of the mean temperature of space, 119; quantity of solar heat received by the earth computed by, 238; data furnished by, to Professor Thomson, 279; development of electricity investi- gated by, 291.
Powell, Baden, substances producing elliptical polarization enumerated by, 193; dispersion of light ac- counted for by the undulatory theory, 200, 201; experiments in transmission of radiant heat, 262; attempts to polarise heat, 264. Power, Mr., undulations producing fluorescent light computed by, 197; law of solar rays acting on media, 198. Præsepe, the, in Cancer, 415.
Precession, a, in the equinoxes of planets, its cause, 66; mean, of the equinoctial points, defined and cal- culated, 80; influence of, on the pole of the equator, on longitudes,
Pressure, electricity elicited by, 283, 284; law of electrical, 288. Principato Citeriore, earthquake in, 234.
Prisms, solar spectrum formed by, 159; neutralizing effects of colour, 164; of brown tourmaline, light polarized by, 180; resolution of the pure white sunbeam by, 222; substance of, determining the point of maximum heat in the solar spectrum, 263, 264; electrical light analysed by, 288.
Problem determining the motions of translation of the celestial bodies, 11; of the three bodies, 58; the hardest astronomical, 92.
Procyon, light of, 402. Proportion, definite, the law of, in
mixing substances, 111, 112. Protoxides of metals, their crystals, 109.
Prussia, Eastern, fulgorites from, 293.
Ptolemy, decrease in the inclination of Jupiter's orbit since the age of, 19; discovery of the Evection by, 35; Indian lunar tables calculated in his time, 88; horoscope ascribed to the age of, 89; effects of refrac- tion observed by, 155; colour of Sirius in his time, 401.
QUADRATURES, the equation of the centre in, 9; lunar orbit augmented in, 35; tides affected by the moon in, 96.
Quadrupeds, distribution of distinct species of, 255. Quartz, crystallised, light polarized
circularly by, 189, 190; varieties of polarization exhibited by, 193. Quebec, extremes of temperature found in, 247.
Quinine, sulphate of, producing fluor- escence of light, 197.
RADIAL force producing periodical changes in relative positions of the heavenly bodies, 15; effects pro- duced by, 16, 17; principle neu- tralising its ultimate result, 19, 20. Radiation of heat, laws regulating, 257; universal from substances, 268; natural phenomena resulting from, 269; slow decrease of the earth's central heat from, 232; influence of, on temperature, 239; power of, in water compared with dry land, 242; of heat, a transfer of motion, 277. Radii vectores, signification of, 8;
areas described by, 10; force dis- turbing in the direction of, 14, 15. Ragona-Scina, M., his theory of ray- less lines in the spectrum, 163. Rain, force shaping drops, 106; cause of periodic tropical, 123; region of, 124; theory of its formation, 270; an electric conductor, 292. Rankine, Mr., his theory of the struc- ture of matter, 104; his theory of the absorption of light, 177. Rays, common nature and common properties of, 268.
of heat, existing independently of luminous, 257; laws of trans- mission of, 258; analogy between transmission of luminous rays and, 259; temperature of their source affecting transmissson, 260; vary- ing in nature with their origin, 261; transmitted through coloured glass, 262; traversing various media, ib.; subject to refraction and reflection, 263; polarized, 265- 267; absorption and reflection of, 268; rotation of polarized, caused by magnetism, 319.
of light, bent by passing from rare into dense media, 153; partial and total reflection of, 156; loss of, by obliquity of incidence, 158; theory of their transmission and absorp- tion, 159-161; comparative refran- gibility of, 163; experiments on dispersion of, 164; principle deter- mining their colour, 170, 171; transmission of, in glass or water,
177, 178; conditions of polarized, 179; double refraction, 181-183; polarized by reflection, 184, 185; coloured images produced by inter- ference of, 194, 195; internal dis- persion of, 195-198; heat, light, chemical action, independent pro- perties of, 214, 215; undulations constituting, 223; conditions mo- difying the power of solar, to pro- duce heat, 237; transmitted inde- pendently of calorific rays, 258; magnetizing of polarized, 318, 319. Rays, solar, effect produced by their refraction in lunar eclipse, 40; passing between lunar mountains in solar eclipse, 41.
of the solar spectrum, their chemical properties, 203; varying chemical energy, 207, 208; varying nature of their action, 208; pecu- liar chemical action of the red, 209-211; deoxydating and oxy- dating action of, 211, 212; expe- riments detailed, 212-215; new, obscure, detected by Sir John Her- schel, 217.
Red Sea, the, tide in, 98. Reflection of waves of sound, 137, 138; of rays at surfaces of strata differing in density, phenomena oc- casioned by, 156, 157; affecting colour, 160; motion of a ray of light in, 177; light polarized by, 184, 185; elliptical polarization produced by, 193; heat polarized by, 266; of radiant heat from surfaces, 268.
Refraction of the sun's rays in lunar eclipses, 40; of waves of sound, 138; of light by the atmosphere, 153, 154; mode of estimating, in case of celestial bodies, 155; for- mulæ obtaining in case of terrestrial objects, ib.; phenomena occasioned by, 155, 156; colours decomposed by, 159, 160; produced without colour, 164, 165; power of, in media affecting the elasticity of the luminous ether, 177; of a polarized ray, 180; double, 181, 182; Fres- nel's theory of, 183; diminished
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