12 



POPULAR SCIENCE MONTHLY. 



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 <? Ursse Majoris. The discovery was made at the Harvard Obser- 

 vatory. Capella is supposed to be another of the same class. 



About 1896 the Lick Observatory was supplied with the best spec- 



Fig. 5. The New Photographic Refracting Telescope of the Astkophysical 

 Observatory at Potsdam, neak Berlin. 



trograph that Brashear could produce, the gifl of Mr. D. 0. [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 tbe radial motion of about one star in every thirteen is affected by 



