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Vapour, formation and dispersion of,
269, 270; force developing, 277.
Variable stars, periodic fluctuation of
lustre in, 390, 391; new, appear
ing and vanishing, 392, 394; miss-
ing, 395.

Variables, region of the, 122.
Vegetation, effect of, in lowering tem-

perature, 243; the two requisites
for, 248; strength and vitality of,
249; chemical action of light in-
fluencing, ib.; laws of its distribu-
tion, 249-252; distribution of
marine, 252, 253; theories of
specific diversity of original distri-
bution of, 253, 254.
Veitch, James, comet with luminous

rings discovered by, 374, 375.
Venus, zone of instability between

the sun and, 21; perturbation in
the mean motion of the earth and,
26; eclipsing Mercury, 42; tran-
sits of, parallaxes calculated from,
52, 53; astronomical tables of, 63;
climate, 226.

Vernal equinox, planetary motions
estimated from, 9.

Vesta, astronomical tables of, 63; no
atmosphere surrounding, 226.
Vesuvius, revived volcanic action of,

Vibrating plates used in experiments

on musical sound, 144, 147.
Vibrations of the air producing sound,
129; in music, 131; number made by
the human voice in a second, 132.

of the ether in natural and po-
larized light, 193; in fluorescence
of light, 196; plane of, in polarized
light, 223.

Vico, Padre de, comet discovered by,


Vienna, observations on comets from,

Vincent, St., revival of an extinct
volcano in, 234.
Virginia, daguerreotyped spectral
image obtained in, 213.
Virgo, planetary conjunction between
Libra and, 42; variable star in,
392; star vanished from, 395;
nebulous zone passing, 416, 417.


Viviers, transit of a comet across the
sun observed from, 374.
Volcanic regions of the globe, 232;
annual number of eruptions, 233;
celebrated eruptions, ib.; earth-
quakes caused by, 234; supposed
causes of action, 235; Sir John
Herschel's theory, 235-237.
Volta, Professor, electricity rendered
manageable by, 297; the world's
debt to, 328.

Voltaic electricity, first suggestions
of, 297; theory of the transmission
of, 298; construction of the bat-
tery, 298, 299; theory of its pro-
duction, 300; characteristic pro-
perties, 300, 301; action of, gene-
rating heat and light, 301-303;
arc, experiments, 303-305; the,
discharge oxidizing silver, 305,
306; stratified light, 306, 307;
chemical decomposition effected by
agency of, 307, 308; crystalliza-
tion, 308; an agent in the fine arts,
309; conductors of, ib. ; relations
of heat and, 310; fish producing
effects of, 310, 311; science sug-
gested by its influence on a mag-
netized needle, 312; rotation ef-
fected by, 313, 314; inducing
magnetism, 314, 315; distinction
between static electricity and, 317;
unvarying dual force of, 334.
Voltaic pile, the, invention of, 297;
perfected, 298-300.

Vortices, molecular, theory of, 104.
Vosges mountains, temperature of
mines in the, 228.
Vulpecula, nebula in, 409.

WARDHUS, transit of Venus observed
at, 53.
Watches, irregular action of, corrected
by the laws of unequal expansion,

Water, constituent parts of, 111;
boiling point of, an estimate of
mountain heights, 120; as a me-
dium for sound, 135; light polar-
ized circularly by, 194; experiment
deciding the velocity of light in,
202; law of expansion of, 271;


process of congelation, 276; boil-
ing points of, 277; decomposed by
electric agency, 307; as an electric
conductor, 309; rotating by elec-
tricity, 314.

Waterspouts, origin and cause of, 128.
Waterstone, Mr., magnetic property

of the ethereal medium maintained
by, 357.

Waves neutralized by interference, 99.
—, atmospheric, over local districts,
periods, dimensions of, 121, 122.

of sound, 131; furnishing an
illustration of reflections of sound
and light, 137; interference of, pro-
ducing calm, 139.

Wedgwood, Dr., attempts of, to trace

objects by means of light, 203, 204.
Week, the, of seven days, the most
ancient and universal division of
time, 85.

Wells, increase of temperature in,
230, 231.

Welsh, Mr., observations made by, in
a balloon ascent, 119.

West Indies, the, cause of hurricanes
in, 126.

Wheels invented to test intensity of
sound, 132, 133.

Wheat, range of its cultivation, 250.
Wheatstone, Professor, experiments in

acoustics of, 132; musical instru-
ments invented by, 143; paper on
musical vibrations read by, 145;
experiments on sounding boards of,
150; experiments on sound rein-
forced by resonance, 151; instru-
ment measuring velocities of elec-
tricity and light invented by, 202;
spectrum of an electric spark ob-
served, 289; speed of electricity
measured, 289, 290; experiments
on the spectrum of Voltaic flame,

Willis, Mr., articulating machine in-

vented by, 151; investigations of,
into the mechanism of the larynx,


Winds, trade, 122, 123; monsoons,
124; extra-tropical, in the North
Atlantic, ib.; currents above the
trade winds, 124, 125; pheno-


mena of rotatory motion, 125;
hurricanes, 125, 128; agency of, in-
fluencing temperature, 244, 245.
Wines, range of cultivation of the
best, 250.

Winter, atmospheric electricity in,

mean temperature of, varying in
the same latitude, 246, 247.
Wolf, Professor, periods of variation
in solar heat computed by, 225.
Wollaston, Dr., experiments of, on
sensitiveness to sound, quotation
from, 132; experiment of, to show
the effect of variable media on re-
fraction, 156; discovery of rayless
lines in the solar spectrum, 162;
observations of, on the chemical
properties of the solar spectrum,
203, 209; magnetic rotation sug-
gested by, 313; light emitted by
the heavenly bodies calculated, 404.

XI Ursa Majoris, periodic time of,
398; velocity of the revolving star,

YEAR, a, in Jupiter and Saturn, 66;
tropical change in its length, 80;
length of the sidereal, ib.; period
of the mean, 83; estimation of the
Egyptian, 85; first of our era, 86;
length of the, affected by a comet's
passage, 359.

Young, Dr., his calculation of the
possible compression of solids, 78;
date of a horoscope determined by,
89; density of a liquid column
estimated by, 114; exception ad-
duced by, to a general law in
acoustics, 137; his theory of the
pleasures of harmony, 142; undu-
latory theory established by, 169;
data used by, to test his theory of
light, 175; illustration of, proving
sound and heat kindred forces, 280,

ZETA Cancri, a triple star, 395;
periodic time of, 398; revolution,
400; colours, 401.


Zeta Herculis, periodic time, eclipse

of, 398; light, 402.
Zinc, seleniate of, effect of tempera-
ture on its crystals, 107; sulphate
of, its crystals boiled in alcohol,

-, electricity communicated to
plates of, 220.

Zodiac, the, signs of, change in their
positions, 80.

Zone of constant temperature in the
atmosphere, 119; laws of storms
in the temperate and torrid, 127,
128; of spots on the sun's surface,
its breadth, 224; of constant tem-


perature below the earth's crust,
228; comparative unequal distri-
bution of land in temperate and
torrid, 244; of fixed stars, 385;
of stars nearest the sun, 390; ne-
bulous, 416; of nebulous patches,
417; of meteoric nebulæ, 423.
Zones of instability of planetary orbits,


of temperature in the ocean,


of vegetation on the Peak of
Teneriffe, 250.

Zoophytes, specific distribution of,




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