i8o REPORTS OF inve;stigations and projects. 



inclosed and, as it does not touch the outer tower at any part, there is no 

 reason to doubt that it will be perfectly stable, even when considerable wind 

 is blowing. The outer tower will carry a dome to cover the instruments at 

 the summit and a small electric elevator to render them accessible. The com- 

 bined spectrograph and spectroheliograph, of 75 feet focal-length, will be 

 mounted in a well, with concrete walls, 10 feet inside diameter, and 78 feet 

 deep, which is already completed. The coelostat has been designed and is 

 under construction in our instrument shop. Work on the combined spectro- 

 graph and spectroheliograph will begin soon. 



In addition to the work of completing and mounting the 60-inch reflector 

 and its accessories, the instrument-shop has constructed the focal-plane spec- 

 trograph and the 18-foot stellar spectrograph, apparatus for enlarging and 

 widening specrta, and other minor instruments, besides doing much work on 

 the 100-inch grinding-machine. 



Work on Mount Wilson has included the heavy labor of opening and re- 

 pairing the road from the valley, which was much damaged by landslides 

 caused by the severe rains last winter; the erection and equipment of a new 

 concrete powerhouse, thoroughly fireproof, provided with a 25-horsepower 

 Fairbanks-Morse gasoline engine, a 17-kilowatt dynamo, etc.; the erection of 

 a new storage-battery house, equipped with a battery large enough to provide 

 power for operating the dome and mounting the 60-inch reflector, the 150- 

 foot tower telescope, and other instruments and machinery. Wooden cottages 

 for the engineer, night assistant, and janitor, and three small houses for 

 night-observers were also constructed. A building for an astrophysical 

 museum has been erected, in which a large collection of photographs illus- 

 trating the work of the Observatory will be open for public inspection. An 

 underground chamber, with concrete walls and roof, has been provided for 

 the variometer, which is now mounted in it. In addition to this work, a 

 concrete laboratory and a small dwelling-house have been built by our con- 

 struction force for the Smithsonian Expedition, and the 150-foot tower tele- 

 scope is now being erected. 



