REPORT OF THE SECRETARY. 85 



Several automatic recording pyrheliometers were raised to great 

 heights in sounding balloon experiments at Omaha early in July, 

 1914. These instruments were all recovered, and the one which made 

 the most successful flight was received back entirely uninjured. A 

 great many experiments were made with it at Washington to inves- 

 tigate certain peculiarities of its record, and to more thoroughly 

 standardize its pyrheliometric and barometric elements. These ex- 

 periments consumed much time of the director and Mr. Aldrich. 

 The results reached from these balloon pyrheliometer records will 

 be summarized below. 



Further experiments were made with sky-radiation apparatus. 



As in former years the major portion of the time of Mr. Fowle 

 and Miss Graves, and a considerable part of ,that of Mr. Aldrich 

 and Mr. Carrington, has been used in measuring and reducing the 

 Mount Wilson holographic data. This work is heavier than for- 

 merly, as it now includes the tower-telescope observations on the dis- 

 tribution of brightness along the sun's diameter. These are now 

 made at seven difl^erent wave lengths of the spectrum on each day 

 that solar-constant measurements are secured. Owing to the de- 

 mands of the Mount Wilson work, Mr. Fowle has devoted but little 

 time to his research on the transmission of long- wave rays in air 

 containing water vapor. 



The instrument maker, Mr. Kramer, was occupied mainly on the 

 construction of sky-radiation apparatus, and on many improvements 

 for the Mount Wilson tower telescope. 



AT MOUNT WILSON". 



Observations by Messrs. Abbot and Aldrich Avere continued at 

 Mount Wilson from July to about November 1, 1914, and were begun 

 again about June 1, 1915. As in former years measurements of solar 

 radiation were made on every favorable day, with the purpose of 

 following the course of the solar variation. On each day of observa- 

 tion the distribution of brightness along the diameter of the solar 

 image of the tower telescope was also observed at seven different 

 wave lengths. 



AT OMAHA. 



As stated in last year's report, Mr. Aldrich, in cooperation with 

 Dr. Blair and other representatives of the United States Weather 

 Bureau, made sounding-balloon experiments at Omaha early in 

 July, 1914. Three flights with automatic recording pyrheliometers 

 were made on July 1, 9, and 11, respectively. The first was made at 

 night, with electric lamps for recording, as a test of certain antici- 

 pated sources of error. In the second flight the instrument was 



