4 CARNEGIE INSTITUTION OF WASHINGTON. 



Mount Wilson Observatory, Geophysical Laboratory, and Department 

 of Terrestrial Magnetism, has continued its course of uninterrupted 

 progress through the past year. Many investigations of importance 

 have been completed and are reported in the lists of publications. 



The program of cooperation of Mount Wilson Observatory with 



California Institute of Technology in an investigation of the structure 



Progress at of matter, as discussed in previous reports, has j ustified 



Mount Wilson itself abundantly by the continuing success of these 

 studies, both in observational and laboratory work at 

 Mount Wilson and in the laboratories of California Institute. The 

 skillfully designed and brilliantly executed plan of Mount Wilson 

 Observatory for investigation of the eclipse of the sun in September 

 failed to secure the tangible results which average conditions would 

 lead one to expect, but the construction of the new 50-foot inter- 

 ferometer, which will extend considerably the possibility for study of 

 fixed stars, was advanced greatly by the need for use of a portion 

 of this mechanism in connection with observation of the eclipse. There 

 is no doubt that great discoveries made possible by the interferometer 

 will be much advanced by this circumstance. Moreover, the splendid 

 spirit with which the staff of the Observatory carried out the plans for 

 observation on this occasion can not help but bring its return in very 

 many ways through the routine of the coming year's work. 



As is indicated in the special report of Mount Wilson Observatory, 

 this year has seen the bringing to fruition of the effort initiated by 

 Dr. Hale some years ago, to construct a ruling machine for the purpose 

 of preparing diffraction gratings to be used in connection with special 

 studies for which the major instruments of Mount Wilson Observatory 

 are particularly adapted. After a long period of construction, in 

 which many peculiar obstacles have been overcome, the ruling machine 

 has finally reached a stage of full success and produces gratings of 

 unusually fine quality. The completion of this and other important 

 mechanical aids, together with additional significant progress in the 

 development of the instruments of Mount Wilson, makes certain a con- 

 tinuing and rapid advance in many of the most fundamental investiga- 

 tions of the immediate future. 



The report of scientific studies completed and of discoveries recorded 

 at Mount Wilson during the present year would include in one direction 

 the rapid development of the study of wire explosions at very high 

 temperatures for comparison with the phenomena studied on the sun ; 

 in another direction the recent discovery that the magnetic polarity 



