STUDY OF CONDITIONS FOR SOLAR RESEARCH 

 AT MOUNT WILSON, CALIFORNIA. 



By George E. Hale. 



In 1902, Dr. S. P. Langley addressed a communication to the 

 Carnegie Institution recommending the estabhshment of an observ- 

 atory at a very high altitude for the special purpose of measuring the 

 solar radiation. In this communication Dr. Langley offered reasons 

 for his belief that the solar radiation may vmdergo changes of in- 

 tensity corresponding with those great changes of solar activity which 

 are so strikingly illustrated in the sun-spot cycle. This communica- 

 tion was 'referred to an advisory committee appointed by the Carnegie 

 Institution to report on various astronomical projects which had been 

 submitted. The committee consisted of Prof. E. C. Pickering, chair- 

 man ; Prof. Lewis Boss, Dr. S. P. Langley, Prof. Simon Newcomb, 

 and the writer. In its report to the Carnegie Institution, the com- 

 mittee expressed its approval of Dr. Langley's proposal and recom- 

 mended, in case the Institution felt inclined to pursue the matter 

 further, that a special committee be appointed to make a detailed 

 report on the requirements of a complete solar observatory. It was 

 also recommended that a project for an observatory in the southern 

 hemisphere be investigated and reported upon by the same committee. 



As a result of this recommendation, a committee, consisting of 

 Prof. Lewis Boss, chairman ; Prof. W. W. Campbell, and the writer, 

 was appointed in December, 1902, to report upon the proposed south- 

 ern and solar observatories. The report of this committee may be 

 found in Year Book No. 2 of the Carnegie Institution. This report 

 also includes a detailed account by Prof. W. J. Hussey of his tele- 

 scopic tests of atmospheric conditions at sites in Southern California 

 and Arizona, where he had been sent hy the committee. Professor 

 Hussey strongly recommended, as the result of his tests, that Mount 

 Wilson, near Pasadena, California, be chosen as the site of the pro- 

 posed solar observatory, in case the Carnegie Institution decided to 

 establish it. 



My first visit to Mount Wilson was made in company with Pro- 

 fessor Campbell in June, 1903. Professor Hussey had practically 

 completed his tests and desired that we should see for ourselves the 

 conditions he had found. Previous observations of the sun at Pike's 

 Peak, Mount Etna, and Mount Hamilton had in no wise prepared me 



155 



