OF ARTS AND SCIENCES. 7 



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--■— = 0".34. Owing to the inclination of the plane of the orbit the 



apparent ellipse would be much less than this. Some other stars 

 would appear better adapted to this test. The smaller difference in 

 light more than compensates for the smaller orbit. From the data 

 given in Table V., the semi-axis major of the ellipse described by 

 several stars has been computed. The name of the star is followed 

 by the time of revolution in years, and the semi-axis of the ellipse de- 

 scribed by the laiger component; y Coronce Australis, 45, 1".2 ; ^ Ur- 

 sce Majoris, 60, 0".8 ; 70 Ophiuchi, 94, 0".4 ; I Bootis, 127, 0".2; 

 Y Virf/inis, 185, 2".0. Some others might give a larger apparent 

 orbit, but a very long time would be required to detect the motion. 

 When the inclination of the orbit is not zero, the apparent ellipse will 

 be less than that comjiuted in this manner in the same proportion that 

 the apparent orbit is less than the real orbit described by the com- 

 panion. Similar observations might be made on any double stars 

 whose components appear to be physically connected. The proper 

 motion, however, complicates the phenomenon, and cannot be distin- 

 guished from the orbital motion as long as the latter appears to be 

 rectilinear. 



So many large telescopes are now devoted to the measurement of 

 double stars that there is great danger of an unnecessary duplication 

 of work. A valuable contribution might be made to our knowledge 

 of stellar motion by determining the positions of the components of a 

 double star with regard to several adjacent stars. Even if the masses 

 of the components could not thus be determined, we should at least 

 provide the material for an accurate measurement of their proper mo- 

 tions in the future. The same may be said of the determination of 

 the proper motions of other stars, which could be observed in this way 

 with much greater precision than by the usual meridian observations. 

 Useful work could be done by an observer unprovided with means for 

 measurements by simply examining a large number of double stars 

 and stars having a large proper motion, and noting the approximate 

 position and distances of any adjacent stars near enough and bright 

 enough for accurate measurement, A list would thus be formed from 

 which the selection of suitable objects would be easy. 



The spectroscope, which has opened so rich a field for work in 

 astronomy, may be applied also to the study of the binary stars. If 

 measurements could be obtained of the approach or recession of the 

 two components, several interesting conclusions could be derived from 

 them. A single measurement would not give the relative masses of 

 the components, since the effect of the proper motion cannot be dis- 



