It is true that a considerable distance on the earth's surface
will seem very small in its effect on the position of a star.
Suppose there were two stars in the heavens, the one in the zenith
of the place where you now stand, and the other in the zenith of a
place a mile away. To the best eye unaided by a telescope those
two stars would look like a single one. But let the two places be
five miles apart, and the eye could see that there were two of
them. A good telescope could distinguish between two stars
corresponding to places not more than a hundred feet apart. The
most exact measurements can determine distances ranging from
thirty to sixty feet. If a skilful astronomical observer should
mount a telescope on your premises, and determine his latitude by
observations on two or three evenings, and then you should try to
trick him by taking up the instrument and putting it at another
point one hundred feet north or south, he would find out that
something was wrong by a single night's work.
Within the past three years a wobbling of the earth's axis has
been discovered, which takes place within a circle thirty feet in
radius and sixty feet in diameter. Its effect was noticed in
astronomical observations many years ago, but the change it
produced was so small that men could not find out what the matter
was.
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