SUNBEAMS.

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 varía-
tions 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; in-
creased 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; pro-
portion of his light to the moon's,
404; rate and orbit of motion with
his system, 405, 406; a nebulous
star, 412; meteoric nebula revolv-
ing round, 422; gravitating force
of, 424, 425.

Sunbeams, resolved into their com-

ponent colours, 159-162; law pre-
vailing 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 cul-
tivation of wheat observed by, 250.
Sympathetic vibrations in musical in-
struments, 147-149.

Syren, the, an instrument ascertaining
the number of musical pulsations in
a second, 143.
Syzigies, tides increased in the, 96.

TABLE-LANDS, high, influence of, on
the atmosphere, 241.
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 photo-
graphy, 204.

Tangent, a, to planetary orbits, planets

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 con-

stellation of, 379; nebula in, 414.
Temperature, a decrease in, affecting
the earth's rotation, 72; excen-
tricity of the terrestrial orbit, a
cause of decreasing, 73; law equal-
ising, 74; geological changes af-
fecting, 75.

-, varying in the terrestrial at-
mosphere, 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; under-
ground stratum of constant, 228;
rate of increase in, below the earth's
crust, 228, 231; of the ocean,
231; mode of finding annual aver-
age, 239; causes of disturbance
in regular variation of, 240-245;
variations in the same latitude,
246, 247; influence of, on vegeta-
tion, 248; affecting transmission
of heat, 259, 260; of solid bodies,
caused by absorption of rays, 268;
affecting the length of the pendu-

TENERIFFE.

lum, 272; causes of perpetual
variations in, 274; transmission of
electricity affected by, 284; affect-
ing 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 varia-
tion, 344; its connexion with solar
magnetism, ib.; effect of atmo-
spheric magnetism on, 345; pro-
bable 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 mea-
suring heat, 333, 334.
Thermography, examples of, 219-

221.

Thermometer, the, principles applied

to the construction of, 113; con-
sulted in determining mountain
heights, 119, 120; refraction vary-
ing with, 154; heat measured by
motion in, 274.

Thermo multiplier, use of, in experi-
ments, 264; principle of its con-
struction, 333, 334.

TOURMALINE.

light, 279; investigation into the
relations of light and magnetism,
320; density of the ethereal me-
dium computed by, 356; magnetic
property of the ethereal medium
pleaded for, 357.

Thunder, theory of prolonged peals of,
138.

Tidal wave, theory of, 92; its birth-
place, 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; ris-
ing, progress of, 93, 94; three
kinds of oscillations in, 95, 96;
variations in, from lunar and solar
influence, 96-98; effect of inter-
ference of waves on, 99; the sea's
equilibrium underanged by, 100.

lunar and diurnal, of the ter-
restrial atmosphere, 121; examples
of sympathetic undulation, 148.
Time, a measure of motion, 58; a
measure of angular motion, 83;
difference between mean and ap-
parent 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 obser-
vations with Hipparchus, 80.
Tomboro, submerged in a volcanic
eruption, 233.

Torpedo, the, electrical action of, 310,

311.

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

Thibet, wheat ripening in, 250.
Thomas, St., the island of, hurricane

with pauses at, 127.
Thomson, W., Professor, experiments
of, in freezing water, 271; dyna-
mical theory of heat maintained
by, 275 note; his calculation of
the force exerted in vibrations of

storms at, 346.

Toucan, comet approaching the con-
stellation of, 379; a nebula in, 414.
Toucani, 47; globular nebulous clus-
ter, 414.
Tourmaline, brown, light polarized
by prisms of, 180; property quali-
fying it to analyze polarized light,
182; coloured images produced by,

SUNBEAMS.

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 varia-
tions 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; in-
creased 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; pro-
portion of his light to the moon's,
404; rate and orbit of motion with
his system, 405, 406; a nebulous
star, 412; meteoric nebula revolv-
ing round, 422; gravitating force
of, 424, 425.

Sunbeams, resolved into their com-
ponent colours, 159-162; law pre-
vailing 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 cul-
tivation of wheat observed by, 250.
Sympathetic vibrations in musical in-
struments, 147-149.

Syren, the, an instrument ascertaining
the number of musical pulsations in
a second, 143.
Syzigies, tides increased in the, 96.

TABLE-LANDS, high, influence of, on
the atmosphere, 241.
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 photo-
graphy, 204.

Tangent, a, to planetary orbits, planets

TEMPERATURE.

impelled in the direction of, 8;
force, disturbing, in the direction of,
14, 15; deflection from, a mea-
surement 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 con-

stellation of, 379; nebula in, 414.
Temperature, a decrease in, affecting
the earth's rotation, 72; excen-
tricity of the terrestrial orbit, a
cause of decreasing, 73; law equal-
ising, 74; geological changes af-
fecting, 75.

-, varying in the terrestrial at-
mosphere, 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; under-
ground stratum of constant, 228;
rate of increase in, below the earth's
crust, 228, 231; of the ocean,
231; mode of finding annual aver-
age, 239; causes of disturbance
in regular variation of, 240-245;
variations in the same latitude,
246, 247; influence of, on vegeta-
tion, 248; affecting transmission
of heat, 259, 260; of solid bodies,
caused by absorption of rays, 268;
affecting the length of the pendu-

TENERIFFE.

lum, 272; causes of perpetual
variations in, 274; transmission of
electricity affected by, 284; affect-
ing 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 varia-
tion, 344; its connexion with solar
magnetism, ib.; effect of atmo-
spheric magnetism on, 345; pro-
bable 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 mea-
suring heat, 333, 334.
Thermography, examples of, 219-
221.

Thermometer, the, principles applied

to the construction of, 113; con-
sulted in determining mountain
heights, 119, 120; refraction vary-
ing with, 154; heat measured by
motion in, 274.

Thermo multiplier, use of, in experi-
ments, 264; principle of its con-
struction, 333, 334.

Theta Orionis, the multiple system
of, 395.

Thibet, wheat ripening in, 250.
Thomas, St., the island of, hurricane

with pauses at, 127.
Thomson, W., Professor, experiments
of, in freezing water, 271; dyna-
mical theory of heat maintained
by, 275 note; his calculation of
the force exerted in vibrations of

TOURMALINE.

light, 279; investigation into the
relations of light and magnetism,
320; density of the ethereal me-
dium computed by, 356; magnetic
property of the ethereal medium
pleaded for, 357.

Thunder, theory of prolonged peals of,

138.

Tidal wave, theory of, 92; its birth-
place, 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; ris-
ing, progress of, 93, 94; three
kinds of oscillations in, 95, 96;
variations in, from lunar and solar
influence, 96-98; effect of inter-
ference of waves on, 99; the sea's
equilibrium underanged by, 100.

lunar and diurnal, of the ter-
restrial atmosphere, 121; examples
of sympathetic undulation, 148.
Time, a measure of motion, 58; a
measure of angular motion, 83;
difference between mean and ap-
parent 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 obser-
vations with Hipparchus, 80.
Tomboro, submerged in a volcanic
eruption, 233.

Torpedo, the, electrical action of, 310,

311.

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

Torronto, observations on magnetic
storms at, 346.

Toucan, comet approaching the con-
stellation of, 379; a nebula in, 414.
Toucani, 47; globular nebulous clus-
ter, 414.

Tourmaline, brown, light polarized
by prisms of, 180; property quali-
fying it to analyze polarized light,
182; coloured images produced by,

TRADE.

186, 187; changed by compression,
189; heat polarized by, 265; elec-
tricity communicated to, 284.
Trade winds, friction of, not affecting

the earth's velocity, 72; action on
the general motion of the sea, 100;
system of, accounting for atmo-
spheric anomalies, 120; theory
of their origin, phenomena con-
nected with, 122, 123; becoming
monsoons, 124.

Transits of Venus, 52, 53.

two consecutive, of any star, a
measure of time, 83.
Transmission of radiant heat, 258,
262; of electricity, 284, 285; of
voltaic electricity, 298; molecular
structure affecting, 303; method
of, determining the influence of
electric currents, 317; of gravity,
an unsolved question, 355; pro-
bable agent, 356; medium of, in
space, 424.

Transparent bodies, temperature of,
unaffected by the sun's rays, 227.
Trees, number of species of forest,
found in America and Europe, 252.
Tribes, apparently distinct, of the
human race, 255.

Triple stars, 395; periods of revolu-
tion in, 400.

Tropical year, change in its length,
80; period of, 83; difficulty of
adjusting its estimation, 85.

revolution of the major axis of
the solar ellipse, its period, 86.

vegetation, the luxuriance of,

248.

Tuileries, clock in the, showing deci-

mal time, 84.

Twilight, caused by refraction, 154;
effect of reflection, 158.
Tyndall, Professor, his experiments
proving diamagnetic polarity, 348;
on magnetic action in crystals, 349.

UNDULATIONS, theory of, 99; of the
atmosphere, 121, 122; of the
waves of sound, 129, 130; inter-
vals produced by interference, 139;
giving musical notes, 142, 143;
sympathetic, 147, 149; of the

VALZ.

luminous ether, 169, 170; in re-
fraction and reflection, 177; pro-
ducing fluorescence, 197; different,
in light and sound, 199, 200; con-
stituting a sunbeam, 223; heat
propagated by, 267; of light, evolu-
tion of latent force in extinguished,
279, 280; of natural forces identi-
cal, 281.
Undulatory theory of light, 168-170;
law of motion affecting, 176, 177;
phenomena proving, 198; objection,
from the different action of light
and sound, refuted, 199; proving
the existence of the ethereal medium,
358; acceleration in comet's mo-
tion proving, 367.

theory, experiments determin-
ing in favour of, 200, 201; final
and decisive experiment, 202; of
heat, 267.

Unison, note in, 142.

United States, astronomical observa-
tions made in, 371, 373.
Uranium, phosphorescent property of,
296; peculiar luminous properties
of, 296.

Uranus, effect of reciprocal attraction
between Neptune and, 22; periods
of the revolutions of his satellites,
33; distance from the sun, 54;
astronomical tables of, 60; disco-
very suggested by his perturbations,
61; observations on, leading to
Neptune's discovery, 62; sun's in-
fluence in, 225; action of, on Hal-
ley's comet, 363; appearance of the
sun to, 380, 381; comets in his
orbit, 381, 382.

Ursa Major, periodic time of a double

star in, 398; nebulous region of, 417.
Utah, deserts of, causing monsoons,

124.

VACUUM produced by shell-fish, 117;
existing in the air, 118.
Valz, M., telescopic planet discovered
by, 21; comet observed by, 358;
observations on a comet's approach
to the sun, 364; cause assigned
by, for contraction in diameter of
comets, 377, 378.