Page:Sir William Herschel, his life and works (1881).djvu/159

Rh one star about the other as a centre—or it might simply be that one star was moving by its own proper motion, and leaving the other behind. It was best to wait and see. The first Catalogue of Double Stars contained two hundred and three instances of such associations. These were observed from time to time, and new pairs discovered. The paper of, "An Inquiry into the probable Parallax and Magnitude of the Fixed Stars, from the Quantity of Light which they Afford, and the Particular Circumstances of their Situation" (1767), was read and pondered. By 1802 had become certain that there existed in the heavens real pairs of stars, both at the same distance from the earth, which were physically connected with each other. The arguments of have been applied by  to the case of one of  double stars, in much the same order in which the argument ran in  own mind, as follows:

The star Castor (α Geminorum) is a double star, where A is of the second, and B of the fourth, magnitude. To the naked eye