234 CARNEGIE INSTITUTION OF WASHINGTON. 



Over 40 per cent of the work of the instrument shop has been con- 

 nected with the 100-inch telescope, the construction of the three 

 additional mirror cages being the largest single item. Among other 

 important undertakings, reference may be made to the following: 

 attachments to Snow coelostat and to 30-foot spectrograph for the 

 Snow telescope, auxiliary apparatus for the 10-inch refractor, a stellar 

 comparator, pressure arc, vacuum pump, diamond polishing-machine, 

 dividing engine, and two small grinding and polishing machines for 

 optical work. Since July 1 almost the entire time of the instrument 

 shop has been given to the construction of precision micrometers for 

 the use of the Government. 



ONE-HUNDRED-INCH TELESCOPE. 



The completion of the building and dome for the 100-inch telescope 

 in the summer of 1916 left the erection of the mounting as the chief 

 outstanding problem in connection with the instrument. This has 

 been in progress throughout the 3'ear under the direction of Mr. 

 Sherburne. For reasons given in the last report, it was impracticable 

 to assemble completely the mounting at the Fore River Works. As 

 a result it has been necessary to proceed rather slowly with the erec- 

 tion and to fit and drill many of the members. Good progress has 

 been made, however. The pedestals, mercury tanks and floats, the 

 polar axis, and the tube are in place, and the rotation of the instrument 

 on its bearings has been tested. The right ascension and declination 

 slow and fast motions have been completed and attached, the large 

 driving worm-wheel has been cut and partially ground, the mirror cell 

 has been fitted, and the support system installed. The Cassegrain 

 cage has been riveted together and ground true, and the mirror elevator 

 has been assembled and tested. Although the work of erection must 

 necessarily be somewhat delayed by the pressure of work in the Pasa- 

 dena instrument shop, we hope to have the telescope ready for tests 

 during the autumn. 



The difficult and complicated task of wiring the instrument and 

 dome, and the construction of the switchboards and much control appa- 

 ratus of special design, has been in charge of Mr. Dowd, our engineer. 



OTHER CONSTRUCTION WORK. 



Two important pieces of construction work have been carried on 

 under the supervision of Mr. Jones. The first was the addition to 

 the Pasadena physical laboratory, completed during the winter. The 

 crowded condition of the building and the necessity of providing space 

 for additional apparatus have been recognized for several years. For- 

 tunately the original building lent itself admirably to an extension and 

 the floor space has thus been nearly doubled. 



The approaching completion of the 100-inch telescope and the ne- 

 cessity of providing for additional observers on Mount Wilson has led 



