216 CARNEGIE INSTITUTION OF WASHINGTON. 



THE OPTICAL SHOP. 



The work in the optical department, which has remained under 

 the direction of Mr. Ritchey, has been much divided. The only large 

 piece of work which has been finished is the Newtonian plane mirror 

 for the 100-inch reflector, the polishing and figuring of which required 

 between 7 and 8 months' time of one of the opticians, Mr. Kinney. 

 In spite of the exceptional difficulties arising from its oval form (the 

 diameters are 24 and 34 inches), a very fine figure has been attained. 

 This mirror is 6)^ inches thick. 



Several months' work has been done by Mr. Dalton on the large 

 oval coude plane mirror for the 100-inch reflector. The greater part 

 of his time, however, has been spent on work for the government. 



In addition, two 12-inch and three 9-inch plane mirrors have been 

 finished for use on Mount Wilson. Two prisms have been made for 

 use with the 13-foot spectroheliograph. 



THE INSTRUMENT SHOP. 



The work of the instrument shop has been under the direction of 

 Mr. Ayers, foreman, while Mr. Jacomini has continued as chief instru- 

 ment-maker. Over one-half of the entire time of the shop has been 

 devoted to the construction of instruments and experimental apparatus 

 relating to war service. Of the remainder, by far the largest part has 

 been given to the 100-inch telescope and its accessories. The most 

 important of these have been the Newtonian, coude, and Cassegrain 

 cages, the observing platform, and the Cassegrain spectrograph. 

 Additional accessories have been the apparatus for silvering and 

 burnishing the 100-inch mirror, two plate-holder attachments, devices 

 for setting the telescope and reading the circles, and many smaller 

 pieces of mechanism. Preparations for the solar eclipse of June 8 

 required rather less than 3 per cent of the working-time of the in- 

 strument shop. 



Twelve outside precision micrometers and eight inside micrometers 

 have been completed for the Bureau of Standards in addition to 

 twelve micrometer heads and a graduated scale. The instrument 

 shop has also constructed much apparatus used in experiments for the 

 Navy and the Signal Corps of the Army. 



Mr. Jacomini has devoted his time to the ruling-engine. The ruby 

 thrust-bearing was finished by the end of 1917, and has been found to 

 perform admirably. The ruling-tests showed the necessity of several 

 minor adjustments, most of which have now been made, so that at the 

 present time the machine is quite free from periodic errors. Investi- 

 gation of errors of run and the very small accidental errors which are 

 still present is now in progress. This involves the ruling of a number 

 of 4-inch gratings, most of which will undoubtedly be useful optical 

 instruments. 



