MOUNT WILSON OBSERVATORY.* 



George E. Hale, Director. 



The fortunate conclusion of the war, followed by the successful tests 

 of the 100-inch Hooker telescope described in this report, mark a dis- 

 tinct epoch in the progress of the Observatory. In returning from 

 war service to our customary field of research,^ and in undertaking 

 systematic observations with this exceptional instrument, we are 

 called upon to survey all aspects of the Observatory's work and to pre- 

 pare a program utilizing in the most effective possible manner the 

 entire instrumental equipment at our disposal. The temptation to 

 embark upon widely scattered investigations, each of great individual 

 promise, but bearing httle relationship to our general scheme of re- 

 search, must be resisted. But this measure of restraint must not 

 involve undue sacrifice of promising ideas or projects suggested by 

 members of the staff or of unique instrumental possibilities. Again, 

 we must steer between the dangers of the atrophy that may result 

 from fixed procedure and endless routine, and the losses inevitable in 

 an unstable and shifting poHcy. To appreciate the problem, and to 

 aid in its solution, we must consider the leading features of the work 

 already accompUshed, evaluate the factors which have determined its 

 present trend, and discern the larger possibihties of our staff and equip- 

 ment in the Ught of recent developments in astronomy and physics. 



The purpose of the Observatory, as defined at the time of its incep- 

 tion, was to undertake a general investigation of stellar evolution, 

 laying special emphasis upon the study of the sun, considered as a 

 typical star; physical researches on stars and nebulse; and the inter- 

 pretation of solar and stellar phenomena by laboratory experiments. 

 It was recognized that the development of new instruments and 

 methods afforded the most promising means of progress, and well- 

 equipped machine and optical shops were provided with this end in 

 view. The determination of stellar positions, parallaxes, and motions, 

 and the study of other problems relating to the structure of the sidereal 

 universe, were not regarded as primary objects in the plan, which had 

 as its central purpose the elucidation of the life-history of a star. While 

 it was obvious that questions of grouping, distance, and velocity are 

 in many cases closely related to those of physical development, it was 

 hoped that the necessary data of this nature would be forthcoming 

 from other sources, leaving us free to concentrate upon the evolutional 

 problem. 



The progress of research, the enlarged possibilities of our instru- 

 mental equipment, and the advantages we have enjoyed from close 



* Situated on Mount Wilson, California. Address, Pasadena, California. 

 ^ The war services of the Observatorj- have been made the subject of a special report to the 

 President of the Carnegie Institution. 



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