35 381 



On common photographs of slars the diameter of the images varies about IV2 

 times as rapidly with the magnitude but tliis would in the present case make the 

 brightest stars inconveniently big if the faint stars are at the same time to be well 

 visible. 



The double and neighbouring stars contained in table 15 have been marked 

 with a short line showing approximately the position angle of the pair. Special 

 attention is called to the group of the 4 stars no' 1003, 1001, 1002, and 998, of 

 which the three first named components are shown as one star on the map. 



I am greatly indebted to the director of the Mount Wilson Observatory, Pro- 

 fessor George E. Hale, who not only immediately granted my request to use the 

 60-inch reflector for the determination of effective wavelengths, but also offered 

 his assistance in realizing my plans. I owe the main part of the necessary funds 

 and five months' leave from Potsdam to the Prussian government and the Academy 

 of Science of Berlin. I wish also to express here my best thanks for the kind and 

 disinterested help given to me by all of the Mount Wilson Observatory staff, not 

 least to Mr. Hoge, the indefatigable night assistant. , 



50* 



