be one in which the radial velocities of the two stars are the same; the lines will then appear single.
The first star of which the binary character was detected in this way is ε Ursæ Majoris. The discovery was made at the Harvard Observatory. Capella is supposed to be another of the same class.
About 1896 the Lick Observatory was supplied with the best spectrograph
Fig. 5. The New Photographic Refracting Telescope of the Astrophysical Observatory at Potsdam, near Berlin.
that Brashear could produce, the gift of Mr. D. O. Mills. In the hands of Campbell the measurements of radial motion with this instrument have reached an extraordinary degree of precision and brought to light the fact that systems of the kind in question are more numerous than would ever have been suspected. Campbell believes that the radial motion of about one star in every thirteen is affected by
