Page 295 - 89 history of astronomy_opt

once. He found two old comets whose or-
bits, in shape and position, resembled the
orbit of a comet observed by himself in 1682.
Apian observed one in 1531; Kepler the other
in 1607. The intervals between these ap-
pearances is seventy-five or seventy-six years.
He then examined and found old records of
similar appearance in 1456, 1380, and 1305.
It is true, he noticed, that the intervals var-
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