MOUNT WILSON SOLAR OBSERVATORY. 267 



truck was placed at our disposal and the difficult work of transporta- 

 tion up the mountain road was commenced last autumn. Several of 

 the larger pieces weigh over 9 tons, but the transportation was carried 

 out without difficulty and the entire mounting, with the exception of 

 the tube sections and the mirror cell, was housed within the 100-inch 

 telescope dome before the opening of the rainy season. 



In the Pasadena shop the work on the smaller parts of the mounting 

 has proceeded rapidly under the direction of Mr. Ayers, and is now so 

 far advanced that no delay from this cause is to be expected in the 

 complete erection of the instrument. The shop work has included 

 the right-ascension and declination slow and fast motions, the coude 

 mechanism, portions of the insulating cover about the mirror cell, the 

 declination counterweight system, and many other auxihary attach- 

 ments. 



The 100-inch telescope dome is now fully completed and painted and 

 the mounting is being erected by Mr. Jones and Mr. Sherburne. The 

 auxihary features of the dome, including observing-platform, jib crane, 

 10-ton travehng crane, and wind screen have been installed, and the 

 two cranes are being utilized in the erection work. The mirror elevator 

 is partially completed. The electric wiring of the dome and instru- 

 ment mounting is nearly finished. As 35 electric motors are in- 

 volved in the motions of the various parts of the telescope and dome, 

 this has been a task of very considerable difficulty. All of this work of 

 wiring, as well as the construction of six switch-boards, has been carried 

 on by Mr. Dowd, engineer in charge of the power-plant. 



OTHER CONSTRUCTION WORK ON MOUNT WILSON. 



With the transfer of the 5-foot spectroheliograph to the 60-foot 

 tower and the increasing demands upon the time of this instrument, it 

 has seemed desirable to adapt the Snow telescope to spectroscopic 

 work of high precision. ^Vccordingly a pit 35 feet deep has been con- 

 structed by Mr. Jones at a distance of 60 feet from the concave mirror, 

 and a vertical spectrograph, of type smiilar to that used in the two 

 tower telescopes, is being built in the Pasadena shop for work within 

 this pit. Slow-motion motor controls are being installed on the coelo- 

 stat and concave mirrors to facilitate guiding during the exposures. 



Other construction work on the mountain has included the installa- 

 tion of a concrete conduit system to carry electric cables between the 

 power-house and the tower telescopes, 60-inch, and 100-inch domes. 

 Work has been commenced on a new telephone line to follow the route 

 of the mountain road. The present line, cheaply built eleven years 

 ago, follows a route very difficult of access in stormy weather, and it has 

 been mipossible to maintain uninterrupted service during the winter 

 months. The portion of the line already installed will obviate some 

 of the most serious difficulties in this respect. 



