MOUNT WILSOX SOLAR 0BSE;RVAT0RY. i8i 



a steel roof. The developing rooms in the basement of the building have 

 been enlarged and reconstructed out of concrete. 



A water-storage reservoir, built of reinforced concrete, with a capacity of 

 140,000 gallons, has been completed. Connected with this is a fire system 

 consisting of 2-inch pipe with hydrants at all of the principal observatory 

 buildings used in conjunction with a high-pressure pump. This should give 

 efficient fire protection for almost any contingency that may arise. 



A new camp house, near the location of the lOO-inch telescope, has been 

 provided for the use of the men engaged in the construction work. Also a 

 storehouse built of sheet iron and a small building which may be used for 

 sleeping quarters during stormy weather. 



The 60-inch reflector dome and the 150- foot tower have been repainted 

 and the canvas around the base of the reflector has been replaced by sheet 

 iron. A small room has been built in the basement of the dome to serve as 

 sleeping quarters for the night observer. 



A 50-horsepower twin-cylinder gas-engine with a direct connected 40- 

 kilowatt generator has been purchased for the power-plant and will be in- 

 stalled during the autumn. This will provide for all the requirements of the 

 entire observatory equipment after the completion of the 100-inch telescope. 



A large amount of general work has been carried on, including the erection 

 of several concrete retaining walls, the laying of conduit for electric power 

 and light, repairs of some of the observers' cottages, and grading at the site 

 of the 100-inch reflector. 



THE 100-INCH TELESCOPE. 



In view of the difficulty experienced by the French Plate Glass Company 

 in securing a thick disk of 100 inches aperture which should be free from 

 air-bubbles and flaws, it seemed advisable in the autumn of 1910 to begin 

 work upon the disk already received and temporarily laid aside. An inspec- 

 tion of this disk had shown that while there were well-defined sheets of air- 

 bubbles running through the body of the glass, they did not approach the 

 surface so closely as to interfere with securing a perfect paraboloidal figure. 

 Furthermore, the glass as a whole seemed to be very firmly knit together, in 

 spite of the presence of the bubbles. Since under these conditions the only 

 obstacle to the perfect success of the disk as an astronomical mirror would 

 lie in the presence of strains in the glass which would prevent it from main- 

 taining its figure under difl:erent conditions of temperature, it appeared well 

 worth the relatively moderate cost of the necessary optical work to investi- 

 gate this question. By the kindness of the French Plate Glass Company the 

 Observatory is permitted to do this work on trial, payment for the disk being 

 conditioned upon its proving suitable for use as an astronomical mirror. 



The process of figuring the disk, although delayed by illness upon the part 

 of those engaged in the work, has been continued steadily, and at the present 

 time the fine grinding of the spherical surface has been completed. As soon 

 as the polishing is finished a series of tests will be undertaken to determine 



