Very small intervals of, 150. Equi-
noctial, 257. 925... Measures, units,
and reckoning of, 906...
Titan, 548., note.

Titius, Prof., his law of planetary dis-
tances, 505., note.
Trade winds, 239...

Transit instrument, 159...
Transits of stars, 152. Of planets
across the sun, 467. Of Venus, 479
Mercury, 483. Of Jupiter's satel-
lites across disc, 540. Of their sha-
dows, 549.

Transparency of space, supposed by
Olbers imperfect, 798.
Transversal disturbing force, and its
effects, 615...
Trigonometrical survey,
Tropics, 93. 380.

Twilight, 44.

U.

274.

Umbra in eclipses, 420. Of Jupiter,

538.

Uranography, 111. 300.
Uranographical corrections, 342... Pro-
blems, 127...

309...
Uranus, discovery of, 505. Heat re-
ceived from sun by, 508. Physical
description of, 523. Satellites of,
551. Perturbations of by Neptune,
760... Old observations of, 760.

V.

Vanishing point of parallel lines, 116.
Line of parallel planes, 117.
Variation of the moon explained, 705...
Variations of elements, 653. Periodical