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single case the general colour of the faint
companion is invariably to be classed with
colours more near to the blue end of the
spectrum than that of the principal star.
Binary Stars. –Sir William Herschel be-
gan his observations of double stars in the
hope of discovering an annual parallax of
the stars. In this he was following a sugges-
tion of Galileo’s. The presumption is that,
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