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peared or disappeared in the interval of 150
years; but he found that all the stars seemed
to have changed their places with reference
to that point in the heavens where the eclip-
ˆ
tic is 90A from the poles of the earth–i.e.,
the equinox. He found that this could be
explained by a motion of the equinox in the
direction of the apparent diurnal motion of
the stars. This discovery of precession of
103