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if there be no physical connection between
the stars of a pair, the largest is the near-
est, and has the greatest parallax. So, by
noting the distance between the pair at dif-
ferent times of the year, a delicate test of
parallax is provided, unaffected by major
instrumental errors.
Herschel did, indeed, discover changes of
distance, but not of the character to indi-
600
