266 CARNEGIE INSTITUTION OF WASHINGTON. 



bination with the finished 100-inch paruboloid and the 60-inch plane 

 mirror while they are being hyperbolized. One of these mirrors is 

 28.75 inches (730 mm.) in diameter and over 6.5 inches (165 mm.) 

 thick. It has a radius of curvature of 346.7 inches (8.81 m.), and gives, 

 with the 100-inch mirror, an equivalent focal length of 1,607 inches 

 (40.8 m.). The other convex mirror is 25 inches (635 mm.) in diameter 

 and 5.5 inches (140 imn.) thick, with a radius of curvature of 274.9 

 inches (6.98 m.) and gives, with the 100-inch mirror, an equivalent 

 focal length of 3,011 inches (76.5 m.). The convex mirrors are now 

 fully polished, each to the nearest spherical surface, and are ready for 

 hyperbolizing. 



WORK OF THE INSTRUMENT SHOP. 



The instrument shop (Air. Jacomini, chief instrument maker; Mr. 

 Ayers, foreman) has been very busy thi'oughout the year. The ruling- 

 machine has absorbed most of Mr. Jacomini's time in the extensive 

 work of final adjustment and testing and the correction of difficulties 

 encountered with the ruby-steel end-thrust bearing. We hope to over- 

 come these by Hghtening the grating-carriage and by refiguring the 

 ruby and improving its mounting. The first grating completed contains 

 95,000 lines, covering an area of 127 by 160 mm. A careful visual and 

 photographic test of this grating, made by Mr. Babcock, shows that its 

 resolving power is high, though some ghosts are present. The syste- 

 matic use of the machine should soon be followed by still better results. 



The numerous parts of the 100-inch telescope mounting have 

 occupied more than half the time of the instrument shop, but other 

 important additions to the equipment have been made. These include 

 parts or attachments for the 10-inch photographic refractor, 60-inch 

 reflector. Snow telescope, 75-foot spectrograph, 30-foot spectrographs 

 of the 60-foot tower and Snow telescopes, 13-foot spectroheliograph, 

 auxiliary concave-grating spectrograph for laboratory, focal-plane and 

 Cassegrain spectrographs and 8 by 10 plate-carrier for 60-inch reflector, 

 measuring-machines, apparatus for optical work on the 100-inch mirror, 

 apparatus for Stark and Zeeman effects, auto truck and instrument 

 repairs, and miscellaneous work of various kinds. 



ONE-HUNDRED-INCH TELESCOPE. 



In view of the conditions prevaiUng at the Fore River works, it 

 seemed undesirable to provide for a complete assembly of the 100-inch 

 telescope mounting in the factory yards. The more important por- 

 tions, however, such as the mercury tanks and floats, the sections of the 

 polar axis, and the main bearings, were fitted together and tested 

 individually, after wliich all parts of the mounting were shipped to 

 Pasadena. The four sections of the tube, being too large for railroad 

 clearances, were sent by steamship to Los Angeles Harbor. Through 

 the cooperation of the International Motors Company, a 6|-ton Saurer 



