212 REPORTS ON INVESTIGATIONS AND PROJECTS. 



completely fireproof. In this room the heliomicrometer will also be mounted. 

 Adjoining are a dark room and a room 13 by 34 feet, for the study of the 

 photographs. A special instrument shop, for the work of precision done 

 by Mr. Jacomini, chief instrument-maker, occupies the west end of the base- 

 ment. Beneath it, under conditions especially favorable for constancy of 

 temperature and stability, is a sub-basement for the ruling machine. 



The very complete heating and ventilating plant is in a small separate 

 building below grade to the north. The arrangements for providing a con- 

 stant supply of pure air to every room, warmed in winter and cooled in 

 summer by passing through a water spray, will be heartily appreciated by 

 the members of the staff. 



CONSTRUCTION WORK ON MOUNT WILSON. 



Some of the most important construction work of the past year has cen- 

 tered about the power-plant and the distributing system on the mountain. 

 During the winter a 50-horsepower Fairbanks-Morse gas-engine was in- 

 stalled, together with a direct-connected generator of 40 kw. capacity. They 

 have now been in operation for several months and have proved most satis- 

 factory, providing ample power for heavy construction work as well as for 

 the regular requirements of the Observatory. The 25-horsepower engine 

 previously employed has been put in efficient condition for use in emergen- 

 cies, and may be run in connection with the larger engine when an exception- 

 ally great amount of power is required. An auxiliary dynamo, or "boos-ter," 

 has been added to the equipment for the purpose of regulating accurately 

 the voltage of current used in charging the storage battery. With the proba- 

 ble exception of storage-battery capacity, the power-plant is now capable of 

 meeting the demands of the erection and operation of the 100-inch telescope. 



The increasing requirements of the 60-inch reflector in the way of elec- 

 trical connections has led us to install a large switchboard in the basement of 

 the building, and to transfer to it all of the control switches. This has added 

 greatly to the convenience of operation of the telescope and has centralized 

 in a valuable way the complex distributing system connected with the instru- 

 ment. The switchboard and automatic control switches were built entirely 

 by the Observatory engineer. 



During the past winter some trouble was experienced from the effects of 

 frost on the water-main which extends from Strain's Camp to the reservoir. 

 Accordingly during the summer the line has been relaid at a depth well 

 below the frost level. In view of the greatly increased capacity available 

 through the completion in 191 1 of the 140,000-gallon reservoir, it seemed 

 desirable to replace the original 1.5-inch pipe with a 2-inch pipe. The orig- 

 inal pipe has been employed as a conduit for the power circuit which op- 

 erates the electric pump at Strain's Camp and is laid in the same trench with 

 the water line. A very important advantage of this system is that the power 

 line, and consequently the pumping-plant, can not be crippled by a forest 

 fire between the Observatory and Strain's Camp. 



