232 CARNEGIE INSTITUTION OF WASHINGTON. 



INTENSITY DISTRIBUTION IN WIDE IRON LINES. 



Preliminary work on this problem has been undertaken by Mr. 

 Babcock by the method of Nicholson and Merton in conjunction with 

 the 30-foot spectrograph. The photographs taken thus far serve to 

 illustrate the technique of the process, but are not definitive. It is 

 planned to adapt the apparatus for use in conjunction with the inter- 

 ference method on account of the high dispersion thus made available. 



SENSIBILITY OF FOUCAULT KNIFE-EDGE TEST FOR OPTICAL SURFACES. 



In an interferometer of the Fabry and Perot type, residual errors in 

 planeness of the optical surfaces accumulate with the multiple reflec- 

 tions and set a definitive limit to the resolving power obtainable. 

 Further improvements in this type of instrument thus depend largely 

 on increase in accuracy of the surfaces and this in turn requires higher 

 sensibility in the methods of testing. An investigation was under- 

 taken by Mr. Anderson and Mr. Babcock to find how far the Foucault 

 test could be relied on for surfaces of any size, with the result that it 

 appears possible to detect a general curvature amounting to only 1/75 

 of a wave-length, without regard to the absolute size of the surface. 

 The investigation was marked by unusual precautions to guard against 

 the introduction of bias on the part of the observers. 



CONSTRUCTION DIVISION. 



DRAFTING AND DESIGN. 



A large proportion of the work of the drafting department has been 

 related to the 100-inch telescope and its accessories. Difficulties con- 

 nected with the operation of the observing platform led to a re-design 

 of this important adjunct to the instrument, and the progress of the 

 erection has necessitated occasional modifications of some of the 

 auxiliary apparatus. The spectrograph for use at the Cassegrain 

 focus has been designed, together with one of the double-slide plate 

 holders. The detail drawings have been completed for the right 

 ascension and declination telescope controls, the two long-focus cages, 

 and the Newtonian cage, with their mirror supports, and many other 

 portions of the mounting and attachments. 



In addition to the 100-inch telescope work, drawings for instruments 

 include the following: 



Comparator for measurement of direct photographs 3.5 inches 

 square. 



Diamond polishing machine. 



Pressure arc. 



Pitch micrometer, 6-inch inside and outside micrometers. 



The drafting department has also made the drawings for extensions 

 to the Monastery and the Pasadena Laboratory. Mr. Pease has con- 

 tinued in charge of this department and Mr. Nicholson has acted as 

 chief draftsman. 



