214 CARNEGIE INSTITUTION OF WASHINGTON. 



season for necessary tests and adjustments of the instruments is due to the 

 efforts of all those associated with it, and especially to the skill and active 

 interest of the members of the force of the instrument shop, who, under 

 the immediate direction of Ayers, have carried it to completion. 



Other work of the year has included the following construction: Measur- 

 ing machine for 4 by 10 inch plates; 3-prism stellar spectrograph ; slow motions 

 for Snow coelostat; driving-clock for small coelostat; spectrograph for testing 

 gratings; new mirror mountings for 20-foot interferometer; thermo-couple 

 spectrograph ; large coude spectrograph. Repairs on our existing instruments 

 have been continued regularly and .work has been done on apparatus for Dr. 

 Michelson's investigations and Dr. Wood's seismological instruments. 



A marked improvement has been made in the driving of the 100-inch tele- 

 scope by planing the large steel cylinder which forms the southern element of 

 the mercury flotation system. Because of great difficulty in obtaining mer- 

 cury at the time the telescope was erected, the clearance between the float and 

 the trough in which it rotates was made as small as possible. As a conse- 

 quence, owing to expansion or contraction of the mounting, the float has 

 occasionally touched the sides of the trough and introduced a periodic error 

 into the motion of the telescope. 



A simple and permanent solution of this difficulty has been found in a 

 reduction in size of the float. A special planing mechanism was designed 

 and attached to the side of the mercury trough, the float being rotated under 

 the cutting tool by the regular driving mechanism of the telescope. The 

 work was done by Kimple and Sam Jones, of the instrument shop, and 

 involved planing an area of about 125 square feet to an average depth of 

 one thirty-second of an inch. The result has been the complete elimination 

 of the error in driving. 



BUILDINGS, GENERAL CONSTRUCTION, AND TRANSPORTATION. 



The principal new work on Mount Wilson has been the erection of a house 

 to provide dining quarters for men engaged in construction work and living 

 quarters for a cook. The house previously used for this purpose will be 

 remodeled to furnish adequate living quarters for the men. In this way the 

 difficulties arising from the use of temporary shelters during inclement 

 weather will be avoided. 



George D. Jones, superintendent of construction, has also carried on 

 much other general work, including retaining-walls and improvements on the 

 mountain road, grading around the new reservoir, painting of the large 

 domes and 150-foot tower telescope, and building repairs in Pasadena. In 

 August he went to Point Loma to superintend the transportation and erection 

 of the apparatus for use at the eclipse. 



Merritt Dowd, engineer on Mount Wilson, and Sidney Jones, assistant 

 engineer, have laid the electrical cables in 700 feet of new conduit line and 

 have made many additions to the electrical equipment of the instruments. 

 They have had complete charge of the maintenance of the power, water, and 

 light services upon which the observational work on Mount Wilson depends. 



Through the aid of a special appropriation, the Observatory was able 

 to purchase during the winter a Holt tractor of the caterpillar type. This 

 has already proved of very great value for grading on the mountain top, 

 transportation on steep grades, and especially for opening the mountain 

 road after heavy snowstorms when the ordinary motor truck can not be used. 



