282 CARNEGIE INSTITUTION OF WASHINGTON. 



back of the mirror. This material has proved so satisfactory that 

 an edge band of the same construction has been made for use with the 

 60-inch mirror on Mount Wilson. 



In preparation for the work of parabolizing the mirror a number of 

 modifications have been made in the grinding machine. The most 

 important of these is that of the large arm carrying the grinding and 

 polishing tools, which has been changed so as to admit of giving straight 

 strokes of variable length. Several wooden polishing tools have been 

 completed in readiness for the parabolization. The 60-inch plane mirror 

 to be used in testing the figure of the larger disk is also entirely finished. 



One other important auxiliary piece of apparatus recently completed 

 is a metal frame carrying knife-edge, light-source, and the plate-holder 

 intended for use in the Hartmann photographic tests. The plate- 

 holder is provided with screw adjustments, so that in case of necessity 

 the observer may guide during the exposures and so avoid distortion of 

 the photographic images due to the settling of the 100-inch mirror upon 

 its edge band. 



Work on the 100-inch mounting has progressed in our instrument 

 shop and at the Fore River shops, where the larger parts are being 

 built under the supervision of Professor Peter Schwamb, acting as our 

 representative. The north and south pedestals and bearings, mercury 

 floats, polar axis, and declination bearings have been nearly completed, 

 and work is in progress on the tube. It is expected that all of this 

 heavy work will be finished and assembled at Fore River in time to 

 permit shipment to Pasadena, by way of the Panama Canal, early 

 in 1915. 



Meanwhile the smaller parts and accessories are being made in our 

 own instrument shop. These involve much work of high accuracy. 

 The driving clock, which is nearly completed, required more than half 

 a ton of bronze castings and nearly 1^ tons of iron castings, in addition 

 to the 2-ton driving weight. The teeth of all the gears in the clock 

 train have been accurately spaced with the aid of circles graduated by 

 Mr. Jacomini. Other parts of this telescope in progress during the 

 year include spectrograph, coude mechanism, mirror-support system 

 and casing, bearings, motor-control apparatus, etc. 



The work of erecting the steel building on Mount Wilson is described 

 below. The dome, which has been set up by the Morava Construction 

 Company at their works in Chicago, will soon be ready for shipment. 

 We hope, under favorable weather conditions, to complete its erection 

 on Mount Wilson next summer, so that the mounting may be set on its 

 pier in the autumn. 



MOUNTAIN TRANSPORTATION. 



The necessity for transporting to Mount Wilson material of large 

 dimensions and great weight for use in the construction of the 100-inch 

 telescope has made it desirable to undertake extensive improvements 



