l86 REPORTS ON INVESTIGATIONS AND PROJECTS. 



(i) A spectrograph with camera and coUimator lenses of 46 cm. focal 

 length and a dense flint-glass prism of 63° angle, for determinations of the 

 radial velocities of faint stars. 



(2) A spectrograph with quartz camera and collimator lenses of 5 cm. 

 aperture and a 60° quartz prism. 



(3) A spectrograph with collimator lens of 46 cm. and a camera-lens of 

 18 cm. focal length used with a 30° crown-glass prism. This instrument has 

 been employed by Mr. Path in observations of the spectra of spiral nebulae, 

 star-clusters, and very faint stars. 



A spectrograph containing a concave grating of 100 cm. radius, for use at 

 the 80- foot focus with the Cassegrain combination of mirrors, has been par- 

 tially completed. A Perot-Fabry interferometer has also been adapted for 

 use in this instrument. 



An 8 by 10 plate-carrier, for direct photography in the lOO-foot Casse- 

 grain focus, was completed in August, and used for the photography of 

 nebulse and for preliminary experiments in the determination of stellar 

 parallaxes. 



The large transmission grating, used with the 60-inch reflector by Pro- 

 fessor Hertzsprung for his determinations of the effective wave-lengths of 

 stars, has been presented to the Mount Wilson Observatory by the Astro- 

 physical Observatory of Potsdam. Our appreciative thanks are extended to 

 Director Schwarzschild for this valuable addition to the resources of the 

 Observatory. 



Other changes and improvements include the installation of a new switch- 

 board, with an improved system of control for all quick and slow motions of 

 dome and telescope ; the addition of an extension to the observing platform ; 

 repairs of the driving-clock, clock-wind motor, and right-ascension quick 

 motion, provision of a motor hoist for the canopy, an automatic safety stop 

 on the dome shutter, observing ladder with elevating seat, etc. 



Direct Photography. 



The following photographs of nebulae and star clusters have been taken 

 by Mr. Pease in the principal focus of the 60-inch telescope : 



Spirals : A''. G. C. 1068, 2683, 2841, 4736, 5005 and 5545, 6412, 6478, 7177. 



Spindles : A^. G. C. 3115, 5866. 



Globular Clusters : A''. G. C. 4147, 5272, 5904, 6205, 6218, 6254. 



Planetary Nebulse : N. G. C. 6804, 6818, 6826. 



Gaseous: N.G.C. 650, 1555 (Hind's variable nebula). 



Several photographs were also made of Nova Geminorum, in the hope of 

 detecting nebulosity. 



The following planetary nebulse were photographed by Mr. Pease with the 

 Cassegrain combination giving an equivalent focal length of 100 feet: 



N. G. C. 6210, 6543, 6572, 6818, 7009, 7662. 



