88 CARNEGIE INSTITUTION OF WASHINGTON. 



(jeorge E. Hale, Yerkes Observatory, Williams Bay, Wis. Grant No. 

 103. For measurements of stellar parallaxes^ solar photos;raphs, 

 etc. (First report is in Year Book No. 2, p. xx.) $4,000. 



Abstract of Report. — This work has been carried on by Dr. Schles- 

 inger, assisted by Miss Ware. The principal purpose of the investi- 

 gation is to utilize the 40-inch telescope of the Yerkes Observatory 

 for measuring the distances of a selected list of stars. The great 

 focal length of the instrument and the possibility of obtaining well- 

 defined stellar photographs with it particularly adapt it for this 

 investigation. 



The preliminary experiments demonstrated that the telescope 

 could be used for photography without a color screen. They also 

 showed that 8 by 10 inch plates would be required for the work. 

 Accordingly, a special measuring machine, large enough to take 

 plates of this size, was ordered from Gaertner and received in De- 

 cember, 1903. The various errors of the machine have been care- 

 fully investigated, and the instrument has proved to be well adapted 

 to its purpose. Of the large number of photographs obtained during 

 the year, 71 have been completely measured for the determination 

 of parallaxes. 



The preliminary reduction of the results indicates that they may 

 be expected to yield very precise determinations of stellar paral- 

 laxes. In the case of the double star Struve P. M. 2164, the 

 differences between the parallaxes of the two stars, amounting to 

 0.03, led to the discovery that the system is a true binary, in spite of 

 the great separation and the faintuess of the two stars forming it. 

 The period of the system is probably between 350 and 400 years. 

 Only two other binary systems are known that have greater separa- 

 tion of the companion stars, and both of these are much brighter 

 than the pair under discussion. The corrected parallaxes for the 

 system, as determined independently by the two observers, are in 

 excellent agreement and have a very small probable error. This 

 and other similar results are of special interest in showing the high 

 degree of precision obtained in photographic measures made with a 

 telescope constructed for visual observations only and employed in 

 the present investigation without a color screen. 



Stellar Photometry. — Mr. Parkhurst has continued his photometric 

 observations with excellent results. In addition to the wedge pho- 

 tometry previously employed, he has had the use of a polarizing 

 photometer kindly loaned by Prof. George C. Comstock, director 

 of the Washburn Observatory. The 6-inch and 24-inch reflectors 



