MOUNT WILSON OBSERVATORY. 253 



DESIGN FOR A NEW PHYSICAL LABORATORY. 



The very crowded conditions of our physical laboratory, and the increasing 

 need of better facilities, have been mentioned in previous reports. No de- 

 partment of the Observatory is more important than its laboratory, which 

 often affords the only possible means of interpreting astronomical results. 

 The absence of any facilities, other than small portable ccelostats, for produc- 

 ing a solar image, is another serious defect of the present laboratory. A new 

 building has therefore been designed, in the hope that funds for its construc- 

 tion may soon become available. 



Among the chief features of the projected laboratory is a 60-foot tower 

 telescope, giving a large solar image in the center of a room about 50 feet 

 square, equipped with special arcs, sparks, electric furnaces, and other light- 

 sources. In a subterranean vault beneath this room is a spectrograph of 

 75 feet focal length, so designed that the collimator can be shortened to 

 50, 30, or 13 feet, and provided with cameras, for use at various angles with 

 the axis of the collimator, of focal length ranging from 45 inches to 75 feet. 

 This powerful instrument, with other special equipment called for in the 

 scheme, would permit our laboratory investigations to be conducted much 

 more effectively than is now possible. 



KILAUEA EXPEDITION. 



A joint expedition from the Geophysical Laboratory of the Carnegie 

 Institution and the Mount Wilson Observatory has been planned by Dr. 

 Day for further chemical and spectroscopic examination of the gases issuing 

 from the crater of Kilauea. Mr. Babcock, who will be the representative 

 from the Observatory, has designed and assembled two small rapid spectro- 

 graphs suitable for use in the field, together with the auxiliary equipment 

 necessary for direct photographs of the spectra of volcanic flames and suitable 

 comparison spectra. Plans were completed for leaving early in June, when 

 a sudden lowering of the lava column removed for the time being all oppor- 

 tunity for making the observations. The volcano has now resumed activity 

 (August) and the expedition is being held in readiness to leave whenever the 

 conditions warrant. 



CONSTRUCTION DIVISION. 



DRAFTING AND DESIGN. 



The work of the department of drafting and design has been carried on 

 during the year by Messrs. Pease, Nichols, and Kinney. Several new instru- 

 ments have been designed and numerous improvements planned for existing 

 apparatus. The more important of these follow. 



For the 100-inch reflector: Concave grating spectrograph; long-focus 

 coude spectrograph; 3-prism spectrograph with telephoto lenses for use in 

 the red; 12-inch reflecting telescope of the Cassegrain type for use as a finder; 

 changes in 20-foot interferometer beam to admit the use of larger mirrors; 

 large shaper for planing the cylindrical floats. 



For the 60-inch reflector: Slitless focal-plane spectrograph for observations 

 of fields of faint stars; redesign of quartz spectrograph for use with a negative 

 lens; modification of counterweight system. 



