tionship between Mizar and Alcor is closer than might be inferred from the mere fact of their contiguity on the sky. Their proximity is not an accident of situation, as is the case in some other instances when two stars happen to lie in nearly the same line of vision. The association of Alcor and Mizar is rendered highly probable from the fact that they move together in parallel directions and the same velocity. But this is the least of the circumstances that gives Mizar its interest. The star itself is a double of the easiest type, and is at the same time of striking interest and beauty. Every possessor of a telescope, large or small, knows Mizar to be one of the most suitable objects wherewith to delight the friends that visit his observatory, by a glimpse at a double star which is both easy to discern and remarkable in character. This is the second noteworthy point about Mizar; but now for the third and last, which is by far the most interesting of all, and has only lately been ascertained by a discovery which will take its place in the history of astronomy as the inauguration of a new process in the study of things sidereal.
Professor Pickering has, as is well known, been extremely successful in obtaining photographs of the spectra of the stars. Sufficient means having been placed at his disposal by Mrs. Draper, he has applied himself with remarkable results to the compilation of the Henry Draper Memorial. The photographs of the spectra of the stars that he has thus obtained exhibit a fulness of detail that some years ago could hardly have been expected even in photographs of the solar spectrum itself. Among the stars subjected to his camera was Mizar, and the photographs of the spectrum of its principal com
