ORBITS.

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,

282.

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.

PARAMAGNETISM.

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

PARATHERMIC.

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.

1

PHOTO-GALVANIC.

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.

412.

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-

POLARIZATION.

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.

286.

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.

QUININE.

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,

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 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.

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,

REFRACTION.

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