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AIB, 23. Mechanical laws for re-

gulating its dilatation and com.
pression ; rarefaction of, 24.
Density of, 25. Refractive power

of, affected by its moisture, 29.
Angle of reflexion equal to that of

incidence, 91.
Angles, measurement of, 82.
Anomalistic and tropical years,

Apparent diurnal motion of the

heavenly bodies explained, 41.
Apsides, their motion illustrated,

Astronomical instruments, 64.

Practical difficulties in the con.
struction of, 65. Observations

in general, 66.
Astronomy, 1. General notions

concerning the science, 9.
Atmosphere, 25. Refractive power

of the, 26. General notions of its
amount, and law of variation, 30.

Reflective power of, 32.
Attraction, magnetic and electric,
236. Of spheres, 237. Solar at

traction, 239.
Azimuth and altitude instruments,


Calendar, 408. Gregorian, 410.

Julian, 412.
Cause and effect, 232.
Celestial refraction, 34. Maps, 157.

Construction of, by observations
on right ascension and declina.
tion, 158. Objects divided into
fixed and erratic, 161. Longi-

tudes and latitudes, 167.
Centrifugal force, 121.
Chronometers, 77.
Circles, co-ordinate, 97.
Clairaut, 128.
Clepsydras, 77.
Clocks, 77.
Comets, their number, 301. Their

tails, 302. Their constitution,
303. Their orbits, 305. Their
predicted returns; Encke's, 308.
Biela's, 309. Their dimensions,

Copernican explanation of the

sun's apparent motion, 194.


Dates, astronomical means of fix.

ing, 414.
Day, solar, civil measure of time,

408. Sidereal, 409.
Definitions of various terms em..

ployed in astronomy, 54.
Diurnal or geocentric parallax, 189.

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Earth, the, one of the principal

objects of the astronomer's con.
sideration; opinions of the an.
cients concerning, 10. Real and
apparent motion of, explained,
12. Form and magnitude of, 14.
Its apparent diameter, 16. A
diagram, elucidating the circular

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form of, 17. Effect of the curva-
ture of, 19. Diurnal rotation of,
38. Poles of, 47. Figure of, 108.
Means of determining with accu.
racy the dimensions of the whole
or any part of, explained, 109.
Meridional section of, 115. Ex.
act dimensions of, 117. Its form
that of equilibrium, modified by
centrifugal force, 120. Local
variation of gravity on its sur-
face, 123. Effects of the earth's
rotation, 127. Correction for the
sphericity of, 149. The point of
the earth's axis, 170. Conical
movements of, 171. Mutation of,
172. Parallelism of, 195. Pro.
portion of its mass to that of

the sun, 290.
Ecliptic, the, 164. Its position
among the stars, 165. Poles of,
166. Plane of its secular varia.

tion, 328.
Elliptic motion, laws of, 187.
Equations for precession and nuta-

tion, 175.
Equatorial or parallactic instru.
Equinoxes, precession of the, 168.

Uranographical effect of, 169.
Excentricity of the planetary orbits,

its variation, 366.
Explanation of the seasons, 195.

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Equant, 99. recessiorect of, orbits,

Lalande, his ideas of the spots on

the sun, 209.
Laplace accounts for the secular

acceleration of the moon, 355.
Latitude, 57. Length of a degree

of, 111.
Level, description and use of, 92.
Light, aberration of, 177. Urano-
graphical effect of, 179. Its velo-
city proved by eclipses of Jupi.

ter's satellites, 297.
Longitudes, determination of, by

astronomical observation, 135.
Differences found by chrono.
meters, 137. Determined by

telegraphic signals, 139.
Lunar eclipses, 225.

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Gay-Lussac, his aeronautic expe.

dition, 23.
Galileo discovers Jupiter's satel.

lites, 296.
Geographical latitudes determined,

Geography, outline of, so far as it

is to be considered a part of

astronomy, 107.
Gravitation, law of universal, 233.
Gravity, local, variation of, 123.

Statical measure of, 125. Dyna.
mical measure of, 126. Terres-
trial, 233. Diminution of, at the
moon, 235. Solar, 240.

Maclaurin, 128.
Maps, construction of, 147. Pro-

jections chiefly used in, 151. The
orthographic, stereographic, and

Mercator's, 151.
Menstrual equation, 289.
Mercators', projection of the

sphere, 153.
Mercury, the most reflective fluid

known, 91.
Meridian, or transit circle, for as.

certaining the right ascensions
and polar distances of objects,

Microscope, compound, 84.
Milky way, 163. 375.
Moon, the, its sidereal period; its

apparent diameter, 213. Its paral.
lax, distance, and real diameter,
214 The form of its orbit, like
that of the sun, is elliptic, but
considerably more excentric; the
first approximation to its orbit,

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6. The bable con Their

215. Motions of the nodes of,
216. Occultations of, 217. Phases
of, 222. Its synodical periods,
223. Revolutions of the apsides
of, 227. Physical constitution
of, 228. Its mountains, 229. Its
atmosphere, 230. Rotation of;
libration of, 231. Diminution of
gravity at the; distance of it
from the earth, 235. Its gravity
towards the earth; towards the
sun, 289. Its motion disturbed
by the sun's attraction, 354. Ac-
celeration of its mean motion;

accounted for by Laplace, 355.
Motion, parallactic, 13. Appear.

ances resulting from diurnal
motion, 14. Real and apparent
motion of the earth described,
172. Of bodies, 233. Laws of
elliptic motion, 238. Orbit of the
earth round the sun in accord.
ance with these laws, 239.
Mural circle, 89.

256. Superior planets, 259. Their
distances and periods, 260.
Method for determining their
sidereal periods and distances,
262. Elliptic elements of the
planetary orbits, 265. Their
heliocentric and geocentric
places, 272. The four ultra.
zodiacal planets, discovered in
1801, 276. The physical peculi.
arities, and probable condition
of the several planets, 277. Their
apparent and real diameters, 280.
Their periods unalterable, 358.
Their masses discovered inde-
pendently of satellites, 371.
Polar and horizontal points, 91.
Pole star, 43. Situation of, 89.
Precession, its physical causes,

Projectiles, motion of, 233. Cur.

vilinear path of, 234.

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Parallax, 48.
Pendulum, 126.
Perturbations, 313. Of the planet-

ary orbits, 340.
Planet, method of ascertaining its
mass, compared with that of the

sun, when it has a satellite, 290.
Planets, the, 243. Apparent motion

of, 244. Their stations and re-
trogradations, 245. The sun
their natural center of motion,
216. Their apparent diameters
and distances from the sun, 247.
Motions of the inferior planets ;
transits of, 249. Elongations of,
251. Their sidereal periods, 252.
Synodical revolutions of, 253.
Phases of Mercury and Mars,
255, Transits of Venus explained,

Satellites, 288. Their motions

round their primary analogous
to those of the latter round the
sun, 291. Of Jupiter, 292. Their

masses, 372.
Saturn, his satellites, 298.
Sea, action of the on the land,

Seasons, explanation of the, 195.
Sextant and reflecting circle, 102

Its optical property, 163.
Sidereal clock, 59.
Sidereal year, 165.
Sidereal time, reckoned by the

diurnal motion of the stars, 59.
Sirius, its intrinsic brilliancy, 379.
Solar eclipses, 218. System, 243.
Sphere, celestial, 35. Projections

of, 151.
Stars, 49. Distance of, from the

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