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earth, 50. Sidereal time reck.
oned by the diurnal motion of
the, 59. Visible by day, 63.
Fixed and erratic, 161. Their
relative magnitude ; infinite
number, 373. Their distribution
in the heavens, 375. Their
distances, 376. The centers of
planetary systems, 380. Period.
ical, 381. Temporary, 383.
Double, 385. Binary, 390. Their
orbits elliptic, 391. Their colours,
394. Their proper motions, 395.
Clusters of, 398. Globular clus.
ters of, 400. Irregular clusters

of, 402 Nebulous, 404
Sun, apparent motion of the, not

uniform, 184. Its apparent dia.
meter also variable, 185. Its
orbit not circular, but elliptical,
186. Variation of its distance,
167. Its apparent annual mo-
tion, 188. Parallax of, 189. Its
distance and magnitude, 192.
Dimensions and rotation of, 193.
Mean and true longitude of, 202.
Equation of its center, 203. Phy.
sical constitution of, 207. Den-
sity of; force of gravity on its
surface, 239. The disturbing
effect of, on the moon's motion,
240.

ferences of declination measured
by, 87.
Terrestrial refraction, 33.
Theodolite, construction of the,

149.
Tides, their physical cause, 335.
Time, measurement of, 77. Its

measures, 408.
Trade winds, 128. Explanation of

this phenomenon, 129. Compens.
ation of, 131.
Transit instrument, 75.
Trigonometrical survey, 147.
Tropical and anomalistic years,

205.
Twilight caused by the reflection

of the sun and the moon on the
atmosphere, 31.

Uranographical problems, 181.
Uranography, 157.
Uranus, his satellites, 299.

V.

Variations, periodic and secular,

341.

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JOHN G. WOLBACH LIBRARY
HARVARD COLLEGE OBSERVATORY

60 GoriD . STREET CAMBRIDGE MASS. 02138

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