Chapter XLV: Section XXXVII (5)

Lightning, development of heat exhibited by, 276, 277;
experiment showing the velocity of, 289;
theory of, 292;
the back stroke, _ib._;
force of the direct stroke, 293;
sheet, 294;
effect of, on the compass, 312.

Lime, carbonate of, variety of form in its crystals, 107;
invariable form ultimately assumed by, 109.

Lines of magnetic force, 338, 339;
experiment ascertaining the form of, 339, 340;
terrestrial, 341, 342;
extensive courses of, 344;
a connected system, 345;
diamagnetic, 348.

Lion, the, conjunction of planets in, 42.

Liquids, balance of forces constituting, 104, 105;
action of capillary attraction on, 113-116.

—— possessing the property of circular polarization of light, 190,
191-193.

Liquids, conditions affecting the transmission of radiant heat by, 263;
evaporation from, 269;
expansion of, by heat, 271;
propagation of heat in, 273;
action of heat as a mechanical force on, 275-277.

London, retarding of the tidal wave between Aberdeen and, 94.

——, pendulum vibrating in its latitude, a standard of measurement, 89;
fulgorites exhibited in, 293.

Long, Dr., his attempt to measure distances of fixed stars, 388.

Longitude, mode of reckoning mean and true, 9;
of the perihelion and of the epoch defined, 10;
cause of periodical perturbations in, 14;
calculation from the moon’s influence on the sun’s, 55;
data of, used in computing a planet’s place in the heavens, 58-60;
change effected by precession and nutation in, 81.

Lloyd, experiments of, in polarization of heat, 264.

Lubbock, Sir John, theory of planetary motion completed by, 64;
his theory of shooting stars, 423.

Lumière cendré, definition of, 227.

Lunar distance, defined, 43.

—— theory, mean distances obtained from, 43.

—— tides of the terrestrial atmosphere, 121.

Lundahles, M., motions of heavenly bodies investigated by, 405.

Lupus, position of, 390.

Lussac, Gay, M., uniting of gases by volumes discovered by, 111;
ascent of, in a balloon, 118;
course of a lightning flash ascertained by, 292.

Lutetia, diameter of, 56.

Lyell, Sir Charles, his theory of changes of temperature in the
northern hemisphere, 75;
annual number of volcanic eruptions computed by, 233;
volcanic phenomena related by, 234.

Lyncis 12, a triple star, 395.

Lyra, a variable star in, 391;
a double star, 395;
nebula, 410.

Machinery, relations of, to force, 353.

Mackintosh, Sir James, quotation from, illustrating the essential
advantages of study, 1.

Maclear, Mr., parallax calculated by, 387.

Madeira, vegetation of, 252.

Madras, Saturn’s ring discovered from, 66.

Magellanic clouds, the, 417, 418.

Magnecrystallic action, 349;
temperature affecting, 352.

Magnetic bodies, difference in power of, 347.

—— elements, the three terrestrial, 343.

—— equator of the earth, 343.

—— meridian, the, mean action of forces determining, 343.

—— poles of the earth, 343.

—— storms, 344;
varying with latitude, 345, 346.

Magnetism, source of, 318;
producing electrical phenomena, 322, 323;
rotatory motion a source of, 330;
classification of substances, with regard to their susceptibility of,
332;
residing in substances after two manners, 335;
experiment illustrating the forces of, 338;
antithesis, its general character, 339;
form of its lines of force, 339, 340;
analogous properties of electricity and of, 340, 341;
terrestrial, 342-347;
connexion between solar and terrestrial, 344;
action of, in crystals, 349-351;
influence of temperature in, 352;
affecting elasticity of matter, 352, 353;
a property of the ethereal medium (?), 356, 357.

——, electro, discovery, importance of the science, 312;
rotation effected by, 313, 314;
electric intensity measured, 315;
action of currents in, defined, 316;
Ampère’s theory of, 317, 318;
causing rotation of polarized rays, 319;
action of, on light, 320;
accidental combinations, 342;
influencing metalliferous deposits, 346.

Magneto-electricity, principle suggesting, 322;
machine constructed on the principle of, 325;
relation of heat to, 329.

Magnets, influence of, on electric light, 307;
fish possessing the power of making, 311;
effect of an electric stream on, 312-314;
obtained by electricity, 315;
power of electro, measured, 315;
cylinders acting as, 316, 317;
producing electrical effects, 322, 323;
evolving electricity by rotation, 330;
classification of substances in relation to, 332;
polarity a property of, 336;
effect on themselves of imparting paramagnetism, 337;
experiment showing the lines of force of, 338;
properties of, indestructible by subdivision, 338, 339;
the earth reckoned among, 342;
planets reckoned among, 346;
action of an electro, on copper, 351.

Maguire, Captain, his observations on magnetic storms, 345, 346.

Malo, St., rising of the tide at, 98.

Malus, M., discovery of polarization of light by, 195;
attempts of, to polarize heat, 264.

Malta, observations on Saturn’s rings made at, 66.

Manchester, thunderstorm near, in 1835, 292.

Mankind, distinct tribes of, 255;
limited perceptions of, 267.

Marcet, M., rate of increase in temperature below the earth’s surface
calculated by, 230.

Marco Polo, atmospheric effects observed by, in ascending mountains,
118.

Marine plants, laws regulating their distribution, 252, 253;
animals, specific localities of, 254.

Mariner’s compass.
_See_ Compass.

Mars, used in illustrating the possible effects of the radial
distributing force, 19;
telescopic planets between Jupiter and, 20, 21;
diameter of, 21;
mean distance from the sun, _ib. note_;
eclipse of Jupiter by, 42;
parallax found by observing his oppositions, parallax of, 53;
internal structure, 58;
astronomical tables of, 63;
climate of, 225;
approach of the comet of 1770 to, 362;
comets having their perihelia in his orbit, 381.

Marseilles, transit of a comet across the sun observed from, 374.

Masses, of the sun, of planets and their satellites, computations
finding, 55, 56.

Mathematics, use of, in the study of astronomy, 2.

Matter, theory of its constitution, 102;
hypotheses as to forces uniting its particles, 103, 104;
counterbalancing action of elasticity and cohesion, 105;
crystallization common to all forms of, 109;
indestructibility of its particles, 110;
composition of unorganised bodies, subject to permanent law, 110,
111;
agent composing or decomposing, 112;
mode of ascertaining the magnetism of, 335;
increatable, indestructible, 353;
proportion of, to spare, 424.

Matteucci, M., effect of electricity on polished silver observed by,
221;
experiment showing polarization by electricity, 286;
doubts of, on the polarity of diamagnetism, 348 _note_;
experiments on magnetic action in crystals, 350;
observation on the action of compression, 352.

Maury, Lieutenant, calms named by, 123.

Measurement of astronomical distances, formula assisting, 43.

Mechain, M., Encke’s comet seen by, 365.

Mechanical equivalent of heat, 275.

—— engines, incapable of generating force, 279.

Mediterranean, the, conditions of, shutting out the tidal wave, 98;
hurricane in, divided into two storms, 126;
vegetation of, 252.

Medium, ethereal, transmitting magnetism, 344;
density of, 356;
probable relations of, to gravity, _ib._;
experiment testing its magnetic properties, 356, 357;
functions of, 357;
pervading the visible creation, 358;
unsolved question touching, 365;
a cause of accelerated revolutions of comets, 366, 367;
direction of its increase in density, 367.

Medium occupying space, 424.

Medusa tribes, the, phosphorescent brilliancy of, 295.

Melloni, M., experiments of, in photography, 214;
his application of the principle of thermo-electricity, 333;
experiments of, in transmission of heat, 258-263;
fixing the maximum of heat in the solar spectrum, 264;
in polarization of heat, 264-266;
light separated from heat by, 265.

Melville Island, height of the thermometer in, in January, 247.

Mercury, inclination of his orbit to the plane of the ecliptic, 21;
eclipse of, 42;
cause of his rotation unknown, 65;
ellipticity of his orbit compared with the terrestrial, 74;
climate of, 226;
comet revolving between the orbits of Pallas and, 367;
attraction of, determining a comet’s orbit, 369;
comets revolving in his orbit, 381;
velocity of, 400.

——, propagation of heat in, 273;
rotating by electricity, 314.

Meridian, constant, of high water, 92.

——, mode of determining the magnetic, 343.

Meridians, size and form of the earth determined from, 46;
measurement of arcs, 47;
anomalies from local attraction, 48;
result of the computations, 48, 49;
permanent, of the moon, 69, 70.

——, magnetic, influencing the direction of metallic veins, 346.

Messier, comet of 1770 observed by, 361;
Encke’s comet seen by, 365;
nebula described by, 409.

Metallic salts, action of the rays of the solar spectrum on, 203.

—— springs used in construction of musical instruments, 143;
rods giving musical notes, 144.

Metallic surfaces, polarized light reflected from, 193;
plates, impressions on, from bodies in contact with, 220.

Metals, expansion of, by heat, 271;
propagation of heat in, 274;
transmission of electricity by, 284;
electricity developed by oxidation of, 298;
determining the appearance of a spectrum of voltaic flame, 303;
distilled in the voltaic arc, 304, 305;
electro-plating of, 309;
properties of, modifying electric susceptibility, 333;
magnetism an agent in the formation of, 346.

Meteor, the bursting of a, 118.

Meteors, 420;
theory of, 421-423.

Meteoric stones, proofs of their foreign origin, 420, 421;
shower of, 421, 422.

Mètre, adopted by the French as their unit of linear measure, 89.

Mica, polarization by induction effected with, 286.

Milky Way, the, described, 385;
Sir John Herschel’s description, 385, 386;
“Coal Sacks,” 386;
stars composing, 286, 287;
zone of stars crossing, 390;
position of variable stars with regard to, 395;
crowding in, apparent only, 405;
orbit in the plane of, 406;
relation of, to the stellar universe, 407;
nebula resembling, 409;
its quarter of the heavens, 414, 415;
dividing the nebulous system, 416, 417;
great nebula in, 418;
remote branches of, 419.

Minerals, possessing the phosphorescent property, 294.

Mines, cause of increased temperature in, 229;
green plants growing in, 253.

Mira, periods of its fluctuations in lustre, 390.

Mirage, supposed cause of, 157.

Miraldi, rotation of Jupiter’s satellite determined by, 70.

Mitscherlich, M., his experiments on crystals, 107;
discoveries, 108;
experiments of, in expansions of crystals, 272.

Mocha, meteors falling at, 421.

Moignot, M., crystals compressed by, 189.

Moisture, an indispensable requisite for vegetation, 248;
transmission of electricity effected by, 284, 288.

Molecular polarity, produced by electricity, 282;
attraction, electricity developed by destruction of, 284.

—— structure affecting transmission of electricity, 303.

—— vortices, hypothesis of, accounting for the absorption of light,
177.

Molecules, material, attraction and repulsion of, 103;
effect of elasticity and cohesion on, 104-106;
uniting to form crystals, 107-109;
extreme minuteness of ultimate, 110;
of ether, modes of their vibration in natural and polarized light,
193;
in fluorescent light, 196, 197;
images traced by the mutual action of, 219-222;
arrangement of, connected with magnetism, 350-352.

Mollusks, distinct species of, 254.

Monocerotis 11, a triple star, 395.

Monsoons, theory of the, 123, 124.

Months, antiquity of, as a measure of time, 85.

Moon, the, force restraining, 4, 5;
mean distance of, from the earth, 4;
results effected by her nearness to the earth, 7;
annual rate of decrease in her orbit’s excentricity, 17;
average distance of, from the earth’s centre, period of her circuit
of the heavens, 34;
her periodic perturbations, 35-38;
causes assigned for acceleration of her mean motion, 36, 37;
eclipses of, 39, 40;
longitudes determined by observations of, 42, 43;
her mean horizontal parallax, 52;
sources whence her mass may be determined, 55, 56;
her diameter, 56;
rotation of, 68;
librations, 69;
mountains, 70;
precession resulting from her attraction, 79-81;
influence of, producing tides, 91, 92, 96-98;
period of her declinations, 97;
atmospheric equilibrium disturbed by her attraction, 121;
cause of her apparent increased magnitude in the horizon, 158;
photographic image of, 214;
comparative amount of light emitted by, 225;
cause of the rarity of her atmosphere, 226;
increased intensity of light at full, _ib._;
effect of the terrestrial atmosphere on heat radiated from, 227;
cause of acceleration in the mean motion of, 366;
light reaching the earth from, 404.

Moorcroft, herbarium collected by, 250, 251.

Moser, Professor, mutual influence of bodies in contact tested by, 219,
220.

Mossotti, Professor, his analysis to prove the identity of the cohesive
force with gravitation, 103, 104;
his definition of gravity, 355.

Motion, a law of the universe, 274;
perpetual, impossible, 279.

Mountains, anomalies in measurement caused by, 48;
rarity of atmosphere on, 118;
cause of perpetual snow, 119;
modes of determining heights of, 120;
becoming new centres of motion in hurricanes, 126;
influence of chains on temperature, 241, 242;
cause of éboulemens in, 271;
tops of, fused by lightning, 293.

——, lunar, effect of solar rays passing between, in eclipses, 41;
influence of, on the moon’s motions, 96;
three classes of, 70.

Mu Herculis, direction of solar motion with regard to, 406.

Multiple systems of stars, 395.

Mundy, Captain, mirage described by, 157.

Music, comparison instituted of sympathetic notes in, 2;
regulated undulations of sound producing, 142;
instruments of, 143;
experiments by means of vibrating plates, 144-146;
sympathetic vibrations, 147, 148;
experiments showing, 148, 149.

Musical instruments constructed by Professor Wheatstone, 143.

Naples, comet discovered from, 370.

Nautical Almanac, computations for calculating longitudes, 43;
time calculated by, 84.

Navigation, importance of lunar motions in, 42;
laws of storms to be observed in, 127, 128.

Neap-tides, 96, 99.

Nebulæ, number and general aspect of, 407;
catalogues, 407, 408;
classes, 408;
irregular, 408, 409;
of definite form, 409;
spiral, 409, 410;
annular, 410, 411;
elliptical, double, 411;
distance of a nebulous star discoverable, 411, 412;
aspect and colour of planetary, 412;
elliptical common, 413;
globular clusters, 413-415;
resolution of, 415;
star clusters, 415, 416;
probable law of motion, 416;
distribution of, 416, 417;
the Magellanic clouds, 417, 418;
round η Argûs, 418, 419;
remote systems, 419;
invisible solar, 421;
meteors falling from, 422.

Nebulous appearances of a comet, 364;
extent of, matter surrounding a comet, 373;
its variable brilliancy, 374;
appearances round the sun, 412.

—— stars, 411, 412.

Needle, magnetized, effect of Voltaic electricity on a, 312, 313;
suspended by means of electricity, 314;
condition of its deviation by an electric current, 317.

Negative electricity defined, 282;
mode of exciting, 283.

—— impressions in photography, 204.

Neptune, periodical variations in his orbit, 22;
revolution of his satellite from east to west, 33;
remoteness of, 54;
anticipation of discovery, 61;
orbit and motions of, determined, 62;
his diameter, mean distance from the sun, 63;
temperature of, 225;
action of, on Halley’s comet, 363.

Neutral phosphate of soda, its crystals, 109.

New Mexico, monsoons occasioned by its deserts, 124.

Newton, Sir Isaac, steps of his argument for the universal influence of
gravitation, 3;
his discoveries of modes of attraction, 4;
motions of bodies projected in space, ascertained by, 5;
form of a fluid mass in rotation ascertained, 45;
problem occupying astronomers since, 64;
discrepancy between his theory of tides and observations, 96;
compound nature of white light proved by, 159;
his analysis of the solar spectrum disputed, 161;
his theory of light disproved, 167;
measurements of coloured rays, 172, 173;
scale of colours, 174;
decisive experiment disproving the theory of light, 202;
remarks on the transmission of gravity, 355.

Niagara, the falls of, not independent of the influence of astronomy,
1.

Nickel, sulphate of, change in its crystals, when exposed to the sun,
107.

Niepcé, M., photographic pictures rendered permanent by, 204;
discovery in photography suggested, 207;
colours of images of the sun taken, 213;
experiments by, on saturation of substances with light, 296.

Nimes, discovery of a telescopic planet at, 21.

Nitrogen, proportion of, in the atmosphere, 117;
spectrum from, 303;
iron volatilized by the Voltaic arc in, 304;
unaffected by magnetism, 344.

Nobili, M., direction of electric currents ascertained by, 333.

Nodes, ascending and descending, of a planet defined, 9;
movement of their lines in secular disturbances, 14;
advance and recession of, 18;
supposed recession of, on the equator of the solar system, 24;
of the moon, period of their sidereal revolution, 37;
secular inequality affecting, 38;
influence of, on eclipses, 39;
cause of their rapid motion, 55;
points of rest on a vibrating string, 141;
in the vibrations of an undulating column of air, 142;
in vibrations of solids, 147.

Non-conductors of electricity, 284, 285.

Non-electrics, 285.

North Atlantic, the, winds in, 124.

—— Polar Ocean, tide in the, 94.

Norway, course of the tidal wave to, 94.

Notes in music, 142, 143.

Nubecula, Major and Minor, 417, 418.

Nucleus, of Halley’s comet, changes in its aspect, 364;
disappearance of, in Encke’s, 369;
division, in Biela’s, 369, 370;
diaphanous, 373;
solidity of, tested, 374;
of a spiral nebula, 409.

Nuremburg, observations on a comet from, 370.

Nutations produced by the moon’s nearness to the earth, 7;
in Jupiter’s equator, 29;
in the planetary axes, 66;
effect of, on the pole of the equator, longitudes and latitudes
altered by, 81.

Nysa, nearness of its orbit to the earth, 21.

Oaks, range of, near the equator, 250.

Occultation, central, by Halley’s comet, 364;
geographical position ascertained by, 384;
prospective, by a sun of α Centauri, 400.

Occultations of stars, 42, 43.

Ocean, the, density and mean depth of, 51;
mean density, compared with the earth’s, 77;
its form in equilibrio, when revolving round an axis, 92;
solar and lunar attraction disturbing its equilibrium, _ib._;
inequalities in periodic motions, 93;
motions of the tidal wave in 95;
stability of its equilibrium, 100;
circulation of currents in, _ib._;
stratum of constant temperature in, 101;
zones of, _ib._;
decrease and increase of temperature with depth, 231;
absorption and radiation of heat by, 242;
electricity evolved from, 291.

Oceans of light and heat, processes producing, 225.

Ochotzk, the sea of, depression of the barometer observed in, 120.

October, 1832, position of Saturn’s rings in, 67.

Olbers, M., computations for a comet by, 367;
period of his comet, 370;
comet of 1811 observed by, 374.

Opaque bodies, mode in which heat is developed in, 227.

Ophiuchi 70, anomalies in the motions of, 400.

Ophiuchus, clusters of the Milky Way between the Shield and, 387;
new star disappearing from, 393.

Optic axis, the, of crystals, 183;
phenomena exhibited by transmission of a polarized ray along, 187,
188;
affected by compression, 189.

Orbit, the, of the earth, attraction intensified by its diminished
excentricity, 37;
excentricity of, affecting temperature, 74, 75;
crossed by comets, 368.

—— of the moon, force ruling, 4;
its excentricity, 34;
changes in, 35;
its inclination to the plane of the ecliptic, 79.

—— of a nebula, 415.

—— of the solar system, 405, 406.

Orbits of comets, subject to variation, 361;
examples, 361-363;
prospective changes in, 369, 370;
of Donati’s, 379;
forces determining their forms, 382, 383.

—— of double stars, 396-400.

—— of planets, force regulating a planet’s velocity in, 8;
measurement of their excentricity, 9;
seven elements of, determining their position in space, 10;
unequal movements in, 15;
variation from elliptical to circular, 17;
secular variations of, in inclination to the plane of the ecliptic,
18, 19;
stable and unstable in form, 21, 22;
influence of the ethereal medium on, 22;
principle facilitating observations on secular inequalities, 23, 24;
revolutions of Saturn compared with Jupiter, 25;
periodic inequality increased by secular variations in their
elements, 26;
comets revolving in, 381, 382;
cause of diversity in form of, 382.

Orbits of satellites, forms of Jupiter’s, 27;
their inclinations, 28;
inclinations 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 Antinous and, 385, 386;
position of, 390;
variable star in, 393, 394;
multiple system in, 395;
nebula in, 408.

Oersted, Professor, discovery of, suggesting the theory of
electro-magnetism, 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 atmospheric, 113;
barometer affected by periodic atmospheric, 120, 122;
of ears of corn, 129, 130;
producing musical notes, 140-142;
instances of forced sympathetic, 148;
causing vicissitudes in climates, 247;
of the pendulum, disturbed by effects of temperature, 272;
measuring variation of electrical intensity, 287.

Otto, M., motions of the heavenly bodies observed by, 405.

Oxidation of metals, electricity developed by, 298;
by the Voltaic discharge on polished silver, 305.

Oxides decomposed by electricity, 307;
alkalies resolved into metallic, 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;
astronomical tables, 63;
ellipticity of its orbit compared with the terrestrial, 74;
height of its atmosphere, 226;
comet revolving between the orbits of Mercury and, 367.

Pan’s pipes, vibrations in the air passing over, 142.

Parabolic motion, ratio of forces procuring, 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;
substances 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 diamagnetism, 347;
neutral substances obtained by combinations of diamagnetism and,
_ib._;
Dr. Tyndall’s experiments on polarity of, 348;
dependent on arrangement of molecules, 350, 351;
affected by compression, 351;
truth establishing its identity with diamagnetism, 356, 357.

Parathermic rays, analyzed by Sir John Herschel, 217-219.

Paris, variation in length of the pendulum at, 51;
mean annual temperature, 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 temperature calculated from observations of, 245;
thermometer at Melville Island marked by, 247.

Pauxis, the Straits of, ebb and flow of the sea in, 98.

Peel, Sir William, thunderstorm experienced by, 293, 294.

Pegasus, nebulous region of, 417.

Pendulum, the, principle equalizing its oscillations, 50;
the earth’s figure calculated by, 50, 51;
experiments ascertaining the earth’s density, 57;
isochronous, a measure of time, 83;
a standard of the measure of extension, 89;
the, a connecting 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 deduced, 24, 25;
of Jupiter’s satellites, 28, 29;
lunar, 35.

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 periodic inequalities, 15;
effects produced by, 18.

Perpetual motion, invariable proportion between heat and force
precluding, 279.

Perseus, variable star in, 390, 391.

Peters, Mr., comet discovered by, 370;
parallax of α Lyræ, 388, 389;
distances of fixed stars calculated, 389;
his theory of Sirius’ irregular motions, 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 computing longitudes, 43;
caused by tidal oscillation, 96;
from force of cohesion, 106, 107;
of capillary attraction, 115;
produced by refraction and reflection, 155-157;
by polarization of light, 186-190;
exhibited in fluorescence of light, 196, 197;
resulting from interaction of rays and molecules, analogous to
effects of photography, 219-222;
phosphorescent, 295, 296;
of galvanism, 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 nebulæ, 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 producing, 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
atmosphere, 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 effects 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, 412.

Planets, paths round the sun described by, 5;
law determining their revolutions, _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;
perturbations 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;
method of computing their places, 58-64;
discovery of, 61-63;
exploded theory touching telescopic, 63;
periods of their rotations, 66;
variation 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 spontaneous 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, 349.

Plumb-line, deviations of, from local attraction, 48;
earth’s density calculated from a deviation of, 58.

Poinsot, M., La Place’s discovery extended by, 23;
comparison by, 24.

Point, ready escape of electricity from a, 288.

Poisson, M., decisions of, on the phenomena of capillary attraction,
114.

Polar basin, probable temperature of, 245, 246.

—— star, change of position in the, 81, 82.

—— vegetation, contrasted with tropical, 248.

Polarity, produced by electricity, 282;
of magnets defined, 336;
induced in iron, 337;
its antithetical manifestations of, 339;
invariably dual, 341;
of diamagnetic substances, 347, 348.

Polarization of light, definition of, 179;
refracted by various substances, 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 producing, 193, 194;
theory of coloured images formed by, 194;
accidental, 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, 286.

——, 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 determining 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 terrestrial, 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 investigated by, 291.

Powell, Baden, substances producing elliptical polarization enumerated
by, 193;
dispersion of light accounted 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 calculated, 80;
influence of, on the pole of the equator, on longitudes, 81.

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 refraction 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 fluorescence of light, 197.

Radial force producing periodical changes in relative positions of the
heavenly bodies, 15;
effects produced by, 16, 17;
principle neutralising 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 disturbing in the direction of, 14, 15.

Ragona-Scina, M., his theory of rayless 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 structure 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 transmission of, 258;
analogy between transmission of luminous rays and, 259;
temperature of their source affecting transmission, 260;
varying 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 absorption, 159-161;
comparative refrangibility of, 163;
experiments on dispersion of, 164;
principle determining 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 interference of, 194, 195;
internal dispersion of, 195-198;
heat, light, chemical action, independent properties of, 214, 215;
undulations constituting, 223;
conditions modifying the power of solar, to produce heat, 237;
transmitted independently 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;
peculiar chemical action of the red, 209-211;
deoxydating and oxydating action of, 211, 212;
experiments detailed, 212-215;
new, obscure, detected by Sir John Herschel, 217.

Red Sea, the, tide in, 98.

Reflection of waves of sound, 137, 138;
of rays at surfaces of strata differing in density, phenomena
occasioned 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;
formulæ 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;
Fresnel’s theory of, 183;
diminished capability of producing fluorescence, 196;
capability of, in rays, affecting their chemical action, 209-212;
effect of, on the lunar atmosphere, 226;
influence of, on transmission of heat, 258;
of rays of heat, 261-264;
heat polarized by, 266.

Refrangibility, substances diminishing, of light, 196;
affecting the chemical 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;
experiments 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 impressions, 166;
comparative sensibility of its fibres to light, 178.

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 lightning, 293.

Richter, variation in length of the pendulum observed by, 51.

Rings of Saturn, 66-68;
Saturn’s, diamagnetic, 347;
luminous, surrounding comets, 374, 375;
surrounding Donati’s, 379.

Ritchie, Professor, electrical experiments 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 increase of temperature in wells
observed 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 atmosphere, 243.

Roget, Dr., phenomena of electro-magnetism explained by, 313.

Rome, observations on lunar mountains 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 discovered by, 410;
nebulous star, 411;
planetary nebulæ, 412;
nebulæ 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 producing electricity, 330-332;
changes produced in comets by, 376.

Rotations of the solar system, 7;
of the sun, 65;
of the planets, 66;
of satellites, 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 substances 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 the 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 attraction upon, 7;
intimate union of, with their primaries, 26;
exceptions 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 affecting 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, 423.

Saturn, unequally occurring compensations of disturbance in its
motions, 15;
disturbing influence of, on Jupiter, excentricity of its orbit
compared with Jupiter’s, 17;
retarding the revolution of Jupiter’s nodes, 19;
invariable plane passing between Jupiter and, 24;
observations on the mean motions of Jupiter 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 discovered by, 249.

Savart, M., his researches and experiments in acoustics, 132, 133;
experiments on vibrations of glass rulers, 145-147;
experiments showing 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 atmospheres 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 occasioned by refraction observed by,
156.

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 unequal 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;
photographic image of the moon obtained, 214;
temperatures of the sun’s surface estimated, 225;
experiments 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;
discovery of, 264;
relations of heat to electricity discovered by, 332, 333.

Seed-lobes, proportion in the distribution of plants having one or two,
252.

Seleniate of zinc, crystals of, 107.

Senarmont, M., experiments of, in expansion of crystals, 273.

Senses, necessarily inaccurate testimony 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, described, 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 impressions, 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 irregular motion, 392;
change in colour, 401;
light, 402;
extent of surface, 404.

Smyth, Admiral, his measurement of Etna compared with Sir John
Herschel’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 modifying the height of the line of perpetual, 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;
equilibrium of, underanged by the ethereal medium, 22;
invariable plane, forming the equator of, 23, 24;
question of its revolution round a common centre, 24;
properties 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 throughout, 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, relative 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, accompanying ringing sound, 147;
expansion 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 illustrated, 129, 130;
conditions modifying the intensity of, musical notes, 131;
experiments testing the compass 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;
reinforced 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;
measuring velocity, 290, 291.

Sounding boards, intensifying musical vibrations, 149;
action of, in musical 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, modified by thickness of the medium absorbing, 160;
decomposed into three colours, 161;
rayless lines in, 162;
observations and experiments on rayless lines, 163, 164;
experiment of fluorescent light, 197;
obtained independently of prismatic refraction, 201;
energetic action of, on matter, 203;
photographic coloured 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 differently from spheres, 4;
force disturbing attraction in, 27;
compression of the terrestrial and of Jupiter’s, computed, 38, 39;
of elliptical strata, quantities invariable 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 probably not independent of, 24;
velocity of light deduced from aberration of, 31;
vast distances of, 54;
precession affecting their longitudes, 80;
computations of their positions furnishing historical data, 88, 89;
made visible by refraction, 154;
peculiar law of light demonstrated 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);
nebulous, 406-419 (_see_ Nebulæ);
seemingly innumerable, 420;
meteors, 420-423.

Static electricity, 282:
_see_ Electricity.

Steam, formation of, 269;
force converting 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 remaining permanently in, 337, 338;
its elasticity affected by magnetism, 352.

Stephenson, George, quotation from, 279-280.

Stokes, Professor, remarks of, on gradation 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 comparative 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 crystals, 108.

Sulphuretted hydrogen gas, its constituent parts, 111.

Sumbawa, volcanic eruption of, 233.

Summer, mean temperature of, varying 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;
importance 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 conjunctions of Jupiter, Saturn, and, 25;
influence of, on lunar motions, 34, 35;
action of the planets reflected 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;
astronomical tables of, 63;
deductions from his rotation about an axis, period of, 65;
attraction of, producing a precession of the equinoxes, 79, 81;
returns of, a measure of time, 83-85;
divisions of time, dependent on revolutions of the major axis of his
orbit, 86, 87;
action on tides, 92, 97;
disturbing the equilibrium 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 surrounding, 212, 213;
his diameter, 224;
appearance of, through his atmospheres, _ib._;
variations in heat and light emitted from, 225, 226;
amount of heat annually received by the earth from, 238;
effect of his brilliancy on the heat emitted by, 259;
his position affecting variations in the magnetic elements, 343, 344;
connexion between periodic variation in his spots and in the magnetic
elements, 344;
vast sweep of his gravitating force, 365;
increased attraction of, for comets, 372;
gulfs separating stars from, 390;
possibility of change in his lustre, 394;
spot on, measured by Sir John Herschel, 394, 395;
proportion of his light to the moon’s, 404;
rate and orbit of motion with his system, 405, 406;
a nebulous star, 412;
meteoric nebula revolving round, 422;
gravitating force of, 424, 425.

Sunbeams, resolved into their component colours, 159-162;
law prevailing in the phenomena of, 198;
light a distinct property of, 214;
resolved into three spectra, 222;
undulations constituting, 223;
their influence on vegetation, 249.

Swan, the, vanishing star in, 393.

Switzerland, meteors falling in, 421.

Syene, arc of the meridian measured between Alexandria and, 49.

Sykes, Colonel, extensive range of cultivation of wheat observed by,
250.

Sympathetic vibrations in musical instruments, 147-149.

Syren, the, an instrument ascertaining the number of musical pulsations
in a second, 143.

Syzygies, tides increased in the, 96.

Table-lands, high, influence of, on the atmosphere, 241.

Tahiti, transit of Venus observed at, 53.

Tail of comets, sudden development of, 372;
forces producing, 375;
unequal illumination of, 375, 376;
change in position of, 376;
divided, _ib._;
constitution of, 377.

Talbot, Fox, his inventions in photography, 204.

Tangent, a, to planetary orbits, planets impelled in the direction of,
8;
force, disturbing, in the direction of, 14, 15;
deflection from, a measurement of centrifugal force, 49.

Tangential force, occasioning secular inequalities, 14;
effects produced by, 15;
producing the variation of the moon, 35;
force acting on the sea, 100.

—— velocity, effects produced by modifications of, 16;
undiminished by the ethereal medium, 22.

Telegraph, the electric, discovery leading to the invention of, 323,
324;
the Atlantic, 325;
principles of its construction, 326, 327;
date of its completion, 327.

Telegraphs, land, principle of their construction, 328.

Telescope, the achromatic, principle of its construction, 164.

——, the differential, differences in illumination determined by, 227.

——, Lord Rosse’s, nebulæ resolved by, 407, 415.

Telescopium, comet traversing the constellation of, 379;
nebula in, 414.

Temperature, a decrease in, affecting the earth’s rotation, 72;
excentricity of the terrestrial orbit, a cause of decreasing, 73;
law equalising, 74;
geological changes affecting, 75.

——, varying in the terrestrial atmosphere, zone of constant, 119;
affecting atmospheric undulations, 121;
modifying the velocity of sound, 134;
chemical action of light affected by, 218-222;
of the ethereal medium, 227, 228;
underground stratum of constant, 228;
rate of increase in, below the earth’s crust, 228, 231;
of the ocean, 231;
mode of finding annual average, 239;
causes of disturbance in regular variation of, 240-245;
variations in the same latitude, 246, 247;
influence of, on vegetation, 248;
affecting transmission of heat, 259, 260;
of solid bodies, caused by absorption of rays, 268;
affecting the length of the pendulum, 272;
causes of perpetual variations in, 274;
transmission of electricity affected by, 284;
affecting magnetism, 352.

Teneriffe, the Peak of, prevailing winds on, 124;
lunar heat on, 227;
zones of vegetation, 250;
character of its flora, 252.

Terrestrial globe, the, a magnet, 336.

—— magnetism, 341-343;
the three elements and their variations, 343, 344;
storms, period of their variation, 344;
its connexion with solar magnetism, _ib._;
effect of atmospheric magnetism on, 345;
probable cause of, 346;
effect of planetary magnetism on, 346, 347.

—— meridian, a, defined, 46.

Tessular system of crystallization, 108.

Texas, monsoons occasioned by its deserts, 124.

Thames, the, period occupied by the tidal wave in reaching, 94.

Thaw, cause of the sensible chilliness of, 276.

Theory of probabilities, use of, in determining astronomical data, 60.

Thermo-electric currents, discovery of, 332;
phenomena exhibited by, 333;
principle of, applied to measuring heat, 333, 334.

Thermography, examples of, 219-221.

Thermometer, the, principles applied to the construction of, 113;
consulted in determining mountain heights, 119, 120;
refraction varying with, 154;
heat measured by motion in, 274.

Thermomultiplier, use of, in experiments, 264;
principle of its construction, 333, 334.

Theta Orionis, the multiple system of, 395.

Thomas, St., the island of, hurricane with pauses at, 127.

Thomson, W., Professor, experiments of, in freezing water, 271;
dynamical theory of heat maintained by, 275 _note_;
his calculation of the force exerted in vibrations of light, 279;
investigation into the relations of light and magnetism, 320;
density of the ethereal medium computed by, 356;
magnetic property of the ethereal medium pleaded for, 357.

Thunder, theory of prolonged peals of, 138.

Tibet, wheat ripening in, 250.

Tidal wave, theory of, 92;
its birthplace, 93;
course of, 93, 94;
velocity, 94;
effect of depth on its motion, 95.

Tides, calculation from the moon’s action on, 55;
theory of forces producing, 91, 92;
circumstances occasioning irregularities, 93;
rising, progress of, 93, 94;
three kinds of oscillations in, 95, 96;
variations in, from lunar and solar influence, 96-98;
effect of interference of waves on, 99;
the sea’s equilibrium underanged by, 100.

——, lunar and diurnal, of the terrestrial atmosphere, 121;
examples of sympathetic undulation, 148.

Time, a measure of motion, 58;
a measure of angular motion, 83;
difference between mean and apparent solar, 84;
mean equinoctial, mode of computing its object, 86;
estimation of, corrected by means of laws of unequal expansion, 272.

Timocharis, comparison of his observations with Hipparchus, 80.

Tomboro, submerged in a volcanic eruption, 233.

Toronto, observations on magnetic storms at, 346.

Torpedo, the, electrical action of, 310, 311.

Torricellian vacuum, experiment on the electric discharge in the, 306;
lines of magnetic force passing through, 344.

Toucan, comet approaching the constellation of, 379;
a nebula in, 414.

Toucani, 47;
globular nebulous cluster, 414.

Tourmaline, brown, light polarized by prisms of, 180;
property qualifying it to analyze polarized light, 182;
coloured images produced by, 186, 187;
changed by compression, 189;
heat polarized by, 265;
electricity communicated to, 284.