210 



CARNEGIE INSTITUTION OF WASHINGTON. 



INVESTIGATIONS IN PROGRESS. 



SOLAR RESEARCH. 

 INSTRUMENTS. 

 The instruments used for solar investigations have remained without 

 material change during the year. The circulating system used to control the 

 temperature of the mirrors of the 150-foot tower telescope has been modijfied 

 sh'ghtly and several attachments have been added to the spectroscopic 

 apparatus. 



SOLAR PHOTOGRAPHY. 



Solar photographs were made with the 60-foot tower telescope during the 

 year ending August 31, 1922, by Messrs. Ellerman, Nicholson, Pettit, E. R. 

 Hoge, and Hickox. They were distributed as follows: 



Photoheliograms of 6.5-inch image, 428 on 280 days. 



Spectroheliograms with 5-foot spectroheUograph (Ha, entire 6.5-inch disk), 203 on 203 days. 



Spectrohehograms with 13-foot spectrohehograph (K and Ho, 2-inch disk and prominences: 

 portions of 6.5 inch disk with Ha and monochromatic light from continuous spec- 

 trum), 788 on 266 days. 



The Snow telescope and the 150-foot tower telescope were used wholly for 



spectrographic and interference observations. 



SUN-SPOT ACTIVITY. 



The number of groups observed during the calendar year 1921 was 140 as 

 against 168 in 1920 and 295 in 1919. Of these, 73 were in northern and 67 

 in southern latitudes. There were 31 days on which no spots were visible 

 at the time of observation, including a period of 9 consecutive days in Novem- 

 ber. The average number of groups observed each day was as follows: 



The average daily number for the year was 2.3, with an average latitude 

 of 10°, as compared with 11° in 1920 and 12° in 1919. 



SUN-SPOT POLARITIES. 



As in previous years, drawings of sun-spots were made daily at the 150-foot 

 tower telescope, showing their positions, polarities, and field-strengths. The 

 following table summarizes the results of these observations: 



