ASTRONOMY — RUSSELL. 89 



Rttssell, Henry N», Princeton, New Jersey. Grant No. 207. Photographic 

 determinations of stellar parallaxes. (For previous report see Year Book 

 No. 3, pp. 92-93.) $1,000. 



Abstract op Report. — Dr. Russell's work was interrupted by illness in the 

 autumn of 1904, and this and its attendant effects with other unavoidable 

 delays prevented him from continuing his work until the spring of 1906. 

 His researches are now in active progress, however, and the present state 

 of the work is as follows : 



The color-screen (consisting of a patch of colored gelatin film upon a 

 plane-glass plate), which was used in photographing bright stars, became 

 useless in the spring of 1905, owing to the contraction of the gelatin, which 

 tore it loose from the glass. This unavoidable accident put an end to the 

 observations of 25 stars, as photographs taken with a new screen would not 

 be strictly comparable with the old ones. Of these stars, 5 had been 

 observed at three parallactic epochs, so that their parallaxes can be deduced 

 in the ordinary way. The photographs of 10 more, which were observed 

 at two epochs only, can be used to give approximate values of their parallax. 

 The remaining 10 stars, observed at one epoch only, are lost to the present 

 work. It may also be necessary to reject one or two others, for which 

 observations at the critical dates were prevented by persistent bad weather. 



Excluding these stars, the total number of available plates obtained up 

 to the date of this report is 252, of 40 different fields. Of these, 226 have 

 either been measured by the writer or are now available for measurement. 

 The remaining 26 have been taken at Cambridge during the past winter by 

 the great kindness of Mr. A. R. Hinks, chief assistant at the Cambridge 

 Observatory, England, and will be forwarded to the writer after some 8 more 

 plates, which are still needed for the full completion of the work, have been 

 obtained ; 122 of these plates, belonging to 32 series, have been measured, 

 and all these have been completely reduced. Under the present circum- 

 stances it is hoped that the larger part of the remaining plates may be 

 measured during the present academic year. 



Six series (for the stars Lalande 21 185, y Virginis, Lalande 25372, Berlin 

 B 5072 and 5073, o Ceti, and /5 Cassiopeiae) have been completed, and least- 

 square solutions made for the parallax. The results are in general highly 

 satisfactory, and show the photographic method to be one of the highest 

 accuracy. 



The results for the first two stars were published in the Monthly Notices 

 of the Royal Astronomical Society for June, 1905. At the same time a 

 brief account of the methods used in the stellar parallax researches at Cam- 

 bridge was published jointly by Mr. Hinks and the writer. 



This work, interrupted by many vicissitudes, has now, through the liber- 

 ality of the observatories at Cambridge and Princeton, every prospect of com- 

 pletion in as satisfactory manner as if no interruptions had occurred. 



