254 CARNEGIE INSTITUTION OF WASHINGTON. 



Miscellaneous: Preliminary sketches and model of 50-foot interferometer; 

 18-inch ccelostat with second plane mirror and driving-clock; designs for 

 apparatus used in the study of the velocity of light and for seismological 

 instruments for Dr. Wood. 



As in previous years, the work of preparing drawings and sketches to illus- 

 trate the publications of the Observatory has been carried on by the drafting 

 department and has required a considerable amount of time. 



OPTICAL SHOP. 



In the optical shop Messrs. Kinney and Dalton have carried on a wide 

 variety of work, including the figuring of glass and speculum mirrors, quartz 

 prisms and plates and numerous small lenses for eyepieces. Included among 

 the mirrors are two 18-inch plane mirrors, two 12-inch plane mirrors of pyrex 

 glass, one 12.5-inch concave mirror of 5 feet focal length with a 3.5-inch hyper- 

 bolic mirror, the whole forming a system of 20 feet equivalent focal length, 

 four small plane and three small concave mirrors, several speculum plates, 

 both plane and concave. In addition, Mr. Kinney has figured one 60° prism 

 and has refigured several other prisms and mirrors. Mr. Dalton has made 

 several quartz plates for use in interference apparatus and thermo-couple 

 work and a plane-parallel plate of glass for the auroral spectrograph. 



GLASS-BLOWING SHOP. 

 Mr. Pompeo has continued to devote part of his time to the construction 

 of glass and quartz tubes for investigations in the laboratory. 



INSTRUMENT SHOP. 



The work of the instrument shop, under the immediate direction of Mr. 

 Ayers, foreman, has included much new construction as well as additions and 

 repairs to existing apparatus. Among the new instruments, partially or 

 wholly completed during the year, are the following : long-focus spectrohelio- 

 graph for experimental purposes, coude spectrograph, large-aperture focal- 

 plane spectrograph, registering photometer, small Cassegrain spectrograph, 

 three-prism spectrograph for work in the red, apparatus for measuring the 

 velocity of light, 12.5-inch finder for 100-inch telescope, numerous plate- 

 holders, and small attachments. 



The section of the 100-inch telescope tube carrying the convex mirror for 

 use in the coude form of the telescope has been fitted into place, and con- 

 siderable work has been done on other accessories of this instrument, includ- 

 ing the wind screen, shutter mechanism, and observing platform. 



RULING MACHINE. 



In last year's report it was stated that the accidental error of the ruling 

 machine appeared to have been removed by the improved spacing mechanism 

 made by Mr. Jacomini. As a test of this a small concave grating of 1 meter 

 radius of curvature was ruled and tested. The definition was excellent, show- 

 ing a satisfactory absence of accidental erorrs, and no ghosts of the Lyman 

 type were found by visual observations. As was to be expected from the 

 known periodic error, the regular or Rowland type of ghost was rather 

 strong. 



The screw pivots were investigated by an interference method and a slight 

 eccentricity was found in one of them. This was reduced as far as it was 



