64 REPORTS ON INVESTIGATIONS AND PROJECTS. 



in the spring. The sun is now photographed every clear morning and 

 afternoon with this spectroheHograph, the daily record comprising photo- 

 graphs taken with the calcium, hydrogen, and iron lines, together with 

 photographs of the chromosphere and prominences in calcium light. In 

 the computing division, organized during the latter part of the year and 

 placed under the direction of Mr. W. S. Adams, provision has been made 

 for the measurement and reduction of these plates. The globe-measuring 

 machine, with which the heliographic latitude and longitude of any point 

 on the sun's disk can be read off directly, thus avoiding the long computa- 

 tions ordinarily required in such work, has been tested and perfected and 

 is now in regular use. It proves to be capable of giving results of high 

 precision, and saves the services of several computers. Further studies 

 of spectroheHograph plates have been made with the aid of the stereo- 

 comparator. These studies have led to some conclusions regarding the 

 comparative level of the calcium and hydrogen flocculi which are described 

 elsewhere in this report. 



Excellent photographs of sun-spot spectra have been obtained with the 

 aid of the Littrow spectrograph, and these have served, in connection 

 with our laboratory studies, in the investigation of the cause of the char- 

 acteristic phenomena of spot spectra. The same instrument has been 

 used by Mr. Adams in a spectrographic investigation of the solar rotation, 

 which has already yielded excellent results. 



The work of our spectroscopic laboratory, of which Mr. Gale has been 

 placed in charge, has proved to be of the greatest value in the interpreta- 

 tion of our solar observations. The need developed in our sun-spot 

 investigations for a 50 K. W. electric furnace has made it necessary to fit 

 up such a furnace, as well as a simple but powerful Littrow spectrograph, 

 in our Pasadena building, because our present power plant on Mount 

 Wilson is not capable of giving so large a current. 



A word should be said as to our further tests of the atmospheric con- 

 ditions on Mount Wilson. The experience derived in three successive 

 seasons has left no doubt of the remarkably high quality of the definition, 

 both for solar and stellar investigations. During the rainy season, as 

 might be anticipated, the definition on the clear days is similar to that 

 experienced under like conditions in the eastern part of the United 

 States. Soon after the close of the rainy season, however, when the 

 weather has settled down to that condition of serenity which is so char- 

 acteristic of California summers, the average definition is remarkably 

 high. The purity of the sky and the perfect calm of many of the nights 

 promise much for the performance of the 60-inch and lOO-inch reflectors. 



The Solar Observatory is glad to take part in the work of the Inter- 

 national Union for Cooperation in Solar Research, which was definitely 



