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Recreations in Astronomy - With Directions for Practical Experiments and Telescopic Work by Henry White Warren
page 95 of 249 (38%)
mighty mountains of Moab removed to reveal the stars of the east.
Train the telescope on any star; it must be moved frequently, or the
world will roll the instrument away from the object. Suspend a
cannon-ball by a fine wire at the equator; set it vibrating north
and south, and it swings all day in precisely the same direction.
But suspend it directly over the north pole, and set it swinging
toward Washington; in six hours after it is swinging toward Rome, in
Italy; in twelve hours, toward Siam, in Asia; in nineteen hours,
toward the Sandwich Islands; and in twenty-four, toward Washington
again, not because it has changed the plane of its vibration, but
because the earth has whirled beneath it, and the torsion of the
wire has not been sufficient to compel the plane of the original
direction to change with the turning of the earth. The law of
inertia keeps it moving in the same direction. The same experimental
proof of revolution is shown in a proportional degree at any point
between the pole and the equator.

But the watchers on the Acropolis do not get turned over so as to
see the moon at the same time every night. [Page 110] We turn down
our eastern horizon, but we do not find fair Luna at the same moment
we did the night before. We are obliged to roll on for some thirty
to fifty minutes longer before we find the moon. It must be going in
the same direction, and it takes us longer to get round to it than
if if it were always in the same spot; so we notice a star near the
moon one night--it is 13° west of the moon the next night. The moon
is going around the earth from west to east, and if it goes 13° in
one day, it will take a little more than twenty-seven days to go the
entire circle of 360°.

[Illustration: Fig. 42.--Showing the Sun's Movement among the Stars.]
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