MOUNT WILSON OBSERVATORY. 213 



various focal lengths at a station near the edge of the shadow at Lakeside, 

 California; third, observations at Mount Wilson with the Snow and tower 

 telescopes of the spectrum of the cusp and of the narrow uneclipsed crescent. 

 Apart from the use of the single large equatorial mounting for all of the instru- 

 ments at the central station, the principal new features of this program will 

 be the attempt to apply the interferometer to a study of the coronal spectrum, 

 and the vacuum thermo-couple to a study of its radiation. The great variety 

 of spectroscopic apparatus and the use of the powerful telescopes on Mount 

 Wilson on the thin crescent are the other main characteristics of the plans 

 which have been developed. 



CONSTRUCTION DIVISION. 



DRAFTING AND DESIGN. 

 The outstanding piece of work in this department, which has been carried 

 on by Pease, Nichols, and H. S. Kinney, has been the detailed design of the 

 mounting and central section of the 50-foot interferometer and its adaptation 

 for use at the solar eclipse. The design of the numerous instruments for 

 the eclipse and of additional equipment for the laboratory and for Mount 

 Wilson has all been planned and worked out in detail with the general assist- 

 ance of the members of the staff. Among the drawings made for these pieces 

 of apparatus are the following: 



Fifty-foot interferometer: Pedestal, polar axis, structural-steel beam, driving-clock and 



worm, fast and slow motions, and general assembly. 

 Eclipse expedition: Assembly of instruments, coronal and stellar cameras, interferometers, 



radiometric apparatus, objective grating, and prismatic spectrographs. 

 For the 100-inch reflector: Thermo-couple spectrograph, ultra-violet spectrograph mounting, 



10-inch lens mounting, brake on right-ascension slow-motion motor, mounting for 



mirrors of 20-foot interferometer. 

 Miscellaneous: Spectroscope for testing gratings, 8-inch by 18-inch comparator, adapter for 



stereocomparator, modification of slow motions on mirrors of Snow telescope. 



Several drawings have been made in connection with the design of the 

 astronomical apparatus for the new building of the National Academy of 

 Sciences at Washington. Drawings and sketches for the publications of the 

 Observatory have been continued, as in previous years. 



OPTICAL SHOP. 



In the optical shop, W. L. Kinney has made several large mirrors and 

 prisms, while Dalton has devoted much of his time to figuring speculum 

 plates for use in the ruling-machine. Among other pieces of optical appa- 

 ratus are the following: A 27-inch paraboloidal mirror for use in radiometric 

 work; a 22-inch paraboloidal mirror and a 4-inch convex to be used as a 

 Cassegrain combination by Dr. Abbot in spectro-bolometric work ; a 60° prism 

 with faces 8 inches by 8 inches; 30 speculum plates for diffraction gratings, 

 and a large number of small prisms, lenses, and plane-parallel plates of quartz, 

 rock salt, alum, and other substances, mainly for use in the laboratory. 



Work in glass-blowing and the manufacture of glass and quartz apparatus 



has been carried on by Pompeo, who has continued to devote a part of his 



time to this purpose. 



INSTRUMENT SHOP. 



The construction of the mounting of the 50-foot interferometer telescope 

 and of the apparatus designed for use at the solar eclipse has made heavy 

 demands upon the instrument shop, especially during the summer months. 

 That this work should have been accomplished successfully and in ample 



