106 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



in fair accord with that of 1920 and 1922. The new results, therefore, 

 now are accepted, and were published immediately after their com- 

 pletion. (Smithsonian Miscellaneous Collections, Vol. 74, No. 7, 

 1923.) 



In the course of this solar energy spectrum work, the observers 

 made solar energy curves with rock-salt prisms at different hours 

 of the day, extending as far down the spectrum as to wave-length 

 14 microns. As yet these observations are not reduced. 



A long and difficult task was undertaken in the observation of the 

 prismatic energy spectra of 10 of the brighter stars in the focus of 

 the 100-inch reflector on Mount Wilson. After much discourage- 

 ment in preparation of apparatus and preliminary trials, successful 

 results were obtained on three nights. The apparatus included a 

 special bolometer and a special galvanometer. Changes of tem- 

 perature of about one one-hundred-millionth of a degree Centigrade 

 were observable, and electric currents of about 10 -12 amperes were 

 read with the galvanometer of 10 ohms resistance. So sensitive was 

 the device that it was affected to an almost incredible extent by 

 electromagnetic induction. It even appeared that the operation of 

 electric power in Pasadena and Los Angeles was effective to cause 

 disturbance through the transmission lines up the mountain though 

 cut off at the power house a thousand feet away from the telescope. 

 Accordingly, best observations were made after 2 o'clock in the 

 morning. The results are given in the paper just cited. 



Field work in Arizona and Chile. — The Mount Harqua Hala sta- 

 tion observed solar variation throughout the year under the efficient 

 direction of Mr. A. F. Moore, assisted until April, 1923, by Mr. F. A. 

 Greeley. Mr. P. E. Greeley, who had been at Montezuma, exchanged 

 places with his brother and reported at Harqua Hala about June 

 8, 1923. 



Mr. L. B. Aldrich assumed the directorship at Montezuma about 

 December 20, 1922, succeeding Mr. L. H. Abbot. At both stations 

 the results of 1923 have been very numerous. They had not yet been 

 critically compared at the close of the period covered by this report. 



RESULTS OF THE WORK ON SOLAR RADIATION 



As long ago as 1903, we found in the observations then being con- 

 ducted in Washington some indication of a variation of the sun's 

 output of radiation. These indications were pursued for several 

 years at Mount Wilson and Mount Whitney, and became so strong 

 that, in 1911 and 1912, expeditions were maintained in Algeria, 

 coincident with one at Mount Wilson, to test whether the supposed 

 solar variations were really of local character. The results seemed 



