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Rotation. The motion of a body round an axis.

Sauri or Saurians. Reptiles of the lizard kind, as crocodiles.

Secular inequalities. Variations in the motions of the heavenly bodies, requiring many ages for their_accomplishment.

Sidereal day. The time included between two consecutive transits of the same star at the same meridian.

Sidereal year. The time included between two consecutive returns of the sun to the same star.

Sine. The perpendicular drawn from the extremity of an arc to the diameter of a circle, c D, (fig. 5,) is the sine of the arc с в.

Solstices. The points in which the sun is farthest from the equator.

Solar spectrum. The colored image of the sun refracted through a prism.

Space. The boundless region which contains all creation. Species of plants. Plants of the same kind.

Sphere. A solid formed by the rotation of a semi-circle about its diameter.

Spheroid of revolution, or Ellipsoid. A solid formed by the revolution of an ellipse about one of its axes. The spheroid will be oblate or prolate, according as the revolution is performed about the minor or major axis of the ellipse. Spheroids are sometimes irregular in their form.

Spiral. A curve like a watch spring. It may be circular, like a thread wound about a round rod; or elliptical, like a thread winding about an oval stick.

Stratum. A layer.

Subtend. To be opposite. In fig. 5, the arc с в subtends the angle C A В.

Sulphate of lime. A mineral capable of being split into thin transparent plates; it consists of 327 of lime, 46.3 of sulphuric acid, and 21 of water.

Synodic revolution of the moon. The time between two consecutive new or full moons.

Syzygies. The points in the moon's orbit where she is new or full.

Tangent. A straight line touching a curve in one point, as T t in fig. 2.

Tangential force. A force in the direction of the tangent.

Time, true. Time shown by a dial, or apparent time. Time shown by ordinary clocks and

Time, mean. watches.

Thermo-electric currents. Streams of electricity, excited by heat.

Transit. The passage of a body across the meridian of a place.

Transit of Venus and Mercury. The apparent passage of these planets across the sun's disc.

Trigonometrical measurements. Mensuration of the surface of the earth by a series of triangles.

Tropical year. The period between the consecutive returns of the sun to the same tropic or solstice.

True distance. The actual distance of a body from the sun, or of a satellite from its planet.

Undulation. A wave.

Undulatory theory. The mechanical principles of the motion of waves.

Vapor. Steam.

Variation. A periodic inequality in the motion of the

moon.

Variation of the compass. The deviation of the compass needle from the true north.

Vertical. The direction of the plumb-line.

Vertical plane. A plane passing through the plumb-line, consequently at right angles to the horizon.

Vesicles. Small hollow spheres of water.

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Visual ray. A ray of light coming from any object to the eye.

Volta-electric induction. The disposition of electric currents to produce similar currents in bodies near them capable of receiving them.

INDEX.

ABERRATION of light, 28
Acceleration of the moon, 34
Action, compound and disturbed,
of the spheres, 14
Air, elasticity of, 73, 104
Airy, Professor, 56, 170, 176
Algæ, 217
Algol, the star, 299
Alps, the, 213

Amazons, river of the, 94
Andes, the, 107

Arabian science, 87

Arago, M., 108, 172, 264
Arcs of the meridian, measure-
ment of, 45, 47
Asia, north-west basin of, 106
Astronomy, physical, 5; divis-
ions of the science of, 57

Astronomical tables, 57
Atmosphere, the, 99, 104, 129, 230
Attraction, its power universal,
5, 10

- and repulsion, electrical,
227, 274

-, capillary, 100
Aurora Borealis, 136, 232, 252
Axis of the earth, 71
Bacon, 29

Barometer, the, 104
Battery, voltaic, 235, 275

galvanic, 237

Biot, M., 168, 269
Birds, 220

Black, or Negro, 221

Bradley, Dr., 77
Cæsar, Julius, 81

Calendar, 80

Caloric, rays independent of
light, 178

from all substances, 187

-combustion, 188

Catalogue of stars by Herschel,
302

Celestial bodies now seen, 130;
phenomena of refraction, 131;
atmospheres of, 196

Centrifugal force opposed to the
law of gravity, 11, 44; its ac-
tion on the sea, 97

Chaldeans, observations by the,
32, 35

Chimborazo, Mount, 47
China, observations made in, 84
Chladni, experiment of, 117
Christian era, the, 81
Chronology of the visible heav-
ens, 300

Climate, 200, 211, et seq.
Coal, 68
Cold, 202, et seq.
[303]
Colors, prismatic, 136, of the stars,
Columbus and Lerius, 218, 243
Comets, theory of, and descrip-
tion of Encke's and other re-
markable comets, 278-295
Compass, the mariner's, 243, 268
Compression, doctrine of, 73
Conductors, electrical, 224

Conjunction of planets, dates of,

39

Connection of the physical sci-
ences, conclusion, 317
Constellations, motion and revo-
lution of, 301

Crystal, 165
Crystallization, 190, 239
Curvature of the earth, 45
Day, the solar and sidereal, 79

-, divisions of, 80, 86

phenomenon of, 187

Fresnel, M., 169, 171
Frost, hoar, 187
Galvanism, 233 et seq.
Galvanometer 256

Geology, 68

Glass, musical vibrations of, 125;

Diameters of the sun and plan- prismatic phenomena, 138, 154;

ets, 56

Diaphanous bodies, 180

Distances in the universe calcu-

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Eclipses, comparison of, 32, 36
-description of lunar, 37

polarization of light by, 160;
impermeable to rays of solar
heat, 179, 182
Gravitation, 314
Gravity, variation in, 42
Gymnotus electricus, 239
Heat, the earth's, 67; solar radi-
ation, 69, 178; of the atmos-
phere, 105; theory, 195
Herbarium, Tartar, 214
Herschel, Sir William, 65, 178,
184, 300

-, Sir John, 117, 289, 298,

304

Herschel, Miss Caroline, 306
Hipparchus, 75

-of Jupiter's satellites is Horizon, its density of atmos-

chronometrical, 27

Ecliptic, the, 75, 82

variation of the, 20
Egyptians, astronomy of the, 85
Elastic bodies, vibrations of, 122
Electricity, science and phenom-
ena of, 222, et seq.
Electrics, Non, 225
Electro-magnetism, 256
Elevation of the earth at the

equator, 41, 49
'Ephemeris,' the, 40
Equator, the, 42, 74
Equinoxes, 75
Eras and chronology, 82, 84
Ether, all-pervading, 278
Ethereal me

medium, the, 145, 170

Eudoxus, 85

Faraday, Mr., 233, 252, 260

Figure of the earth, 41, 47, 85
Fire, production of, 188

Flora, reign of, 212

phere, 135

Horoscopes, accordance with as-

tronomy, 85

Humboldt, Von, 98, 106, 209, 216,

269

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of, 57; density, 78

Kater, Captain, 86

Fluids, properties of, 168, 172, Kepler, theory of, 10, 18, 54, 61

Forests, influence of, 206

Grange
qualities, 20

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