SOIvAR OBSERVATORY. 1 79 



The work of erecting the 6o-inch reflector in its dome was continued 

 through the autumn of 1908 and completed early in December. Great credit 

 is due to Professor Ritchey and all associated with him for the admir- 

 able performance, both mechanical and optical, of this powerful instrument. 

 The excellent design and thorough construction of the mounting have elimi- 

 nated all difficulties which might arise from flexure, imperfect driving, or 

 other causes so commonly encountered in large telescopes. The figure of the 

 mirrors is essentially perfect, and the support system is so satisfactory that 

 the 60-inch mirror is not perceptibly distorted in any position of the telescope. 



The success of the 60-inch reflector seems to leave no doubt that the 100- 

 inch reflector will give still better results, fully in proportion to its increased 

 aperture. Unfortunately, the glass disk, weighing 4.5 tons, which was sent 

 to Pasadena last year, had many defects and was therefore immediately re- 

 jected. The St. Gobain firm had previously supplied us with a large number 

 of disks, up to an aperture of 5 feet, every one of which was perfect, but in 

 this case the flaws within the glass were so numerous that they were seen 

 as soon as it was removed from its packing-case. The management of the 

 glass company immediately expressed their willingness to bear the loss and 

 to construct another disk. Professor Ritchey was sent to Paris to discuss 

 with them the best arrangements for repeating the work, and as the result of 

 his visit a new glass furnace, as well as a new annealing oven and other 

 accessories, were constructed. I examined these at St. Gobain in June just 

 after they were completed, and convinced myself that the preparations for 

 the manufacture of another disk were adequate. At last reports some minor 

 difficulties were still being encountered, but there is every reason to suppose 

 that a perfect disk will soon be obtained. A very fine 60-inch disk, to be 

 made into a plane mirror for testing the figure of the lOO-inch, has recently 

 arrived in Pasadena. The lOO-inch grinding machine will be ready by the 

 time the large disk arrives, and the optical work will be pushed forward 

 without delay. The work of designing the mounting is advancing rapidly, 

 and its construction can be undertaken as soon as funds become available 

 for this purpose. 



The design for the double steel tower of the 150- foot tower telescope was 

 completed by D. H. Burnham & Co., of Chicago, early in June, and the con- 

 tract for the steel let to the Morava Construction Company. All of the steel 

 has arrived in Pasadena and the lower section of the tower is being erected 

 on Mount Wilson. As the coelostat, second mirror, and object-glass are to 

 be supported at a height of 160 feet above the ground, the question of sta- 

 bility is important. To secure protection from the wind (the only source of 

 vibration) each of the steel members of the tower is inclosed within the cor- 

 responding hollow members of a second skeleton tower, mounted on inde- 

 pendent foundations. The tower carrying the instruments is thus completely 



