l66 REPORTS ON INVESTIGATIONS AND PROJECTS. 



Stellar Photography. 



Mr. Fath has taken 3 photographs of the Kapteyn selected areas during 

 the year. Thus far a total of 33 have been obtained since the work was 

 begun, and it should be possible to conclude this series of photographs dur- 

 ing the coming year. Twenty-eight photographs for use in the investigation 

 of the absorption of light in space have been secured during the year. 



Parallax Investigations. 



Seven complete sets of photographs for the determination of stellar paral- 

 lax have been obtained by Mr. Babcock and Mr. Fath under the direction of 

 Professor Kapteyn. Several preliminary photographs have been made with 

 the Cassegrain combination of 100 feet equivalent focal-length. The nega- 

 tives will be investigated carefully during the coming months and future 

 parallax work with the reflector will be guided mainly by the results obtained. 



Photography op Nebula and Star Clusters. 



Mr. Ritchey has continued throughout the year his work with the 60-inch 

 reflector on the photography of nebulas and star clusters. Since the last 

 annual report he has secured photographs of the following objects: 



Spiral nebulae: Messier 33, 51, 63, 64, 81, H. V. 24 Comce Berenices, Andromeda 



Nebula (central part). 

 Planetary nebulae: Owl Nebula, Dumb-Bell Nebula, Planetary Nebula in Draco, 



Planetary Nebula in Hercules. 

 Annular nebulae : Ring Nebula in Lyra, H. IV 13. 

 Irregular nebulae: Messier 82, Orion Nebula (central part), N. G. C. 6960, N. G. C. 



6992, Trifid Nebula. 

 Globular clusters : Messier 3, 13, 92. 



Mr. Ritchey also obtained 17 negatives of the head of Halley's comet in 

 May and 14 negatives in June. 



The exposures on the nebulae and star-clusters have ranged from 3 min- 

 utes on the bright planetary nebulae to 1 1 hours on some of the spiral nebulae 

 and star-clusters. 



The amount of detail shown on these photographs is in many cases extra- 

 ordinarily great, especially in the case of the globular star-clusters and the 

 spiral nebulae. A few of the conclusions drawn by Mr. Ritchey from an 

 examination of the negatives may be summarized as follows : 



(1) The globular star-clusters are found to consist of scores of thousands 

 of stars, and their angular diameters are at least three times as great as they 

 appear in the large refracting telescopes. A partial count by Miss Ware of the 

 number upon an enlargement of a negative of the Hercules cluster up to 

 within 2' of the center gives 27,000 stars. 



(2) The spiral nebulae contain great numbers of star-like condensations 

 which may possibly be stars in process of formation. In general they lie in 

 streams which follow the convolutions of the nebulous material in which 

 they appear. 



