PROCEEDINGS OF THE BOARD OF REGENTS. 113 



Astro physical Observatory. — Solar constant observations were con- 

 ducted by the Astrophysical Observatory at Mount Wilson, Cal., dur- 

 ing the past summer and autumn. Results were obtained showing that 

 the earth's atmosphere is entirely opaque to rays of more than 20 

 microns in wave length and that all such rays were found cut off in 

 a path of 12 feet in air. This is important to meteorology, because 

 about one-fourth of the rays emitted by the earth's surface are above 

 20 microns wave length. 



Expeditionary observations at Hump Mountain, N. C, under a 

 grant from the Hodgkins fund are progressing and will be continued 

 all winter. The work includes measures of the solar constant of radi- 

 ation, measures of the brightness of the sky, measures of nocturnal 

 radiation, and experiments bearing on frost prediction. 



The Astrophysical Observatory is continuing the study of the trans- 

 parency of the air to long-wave rays such as the earth sends out. 

 The atmosphere on clear days appears to transmit onl} r about 20 to 

 30 per cent of the earth's rays outward to space, the quantity trans- 

 mitted decreasing as humidity increases. 



The reduction of the Mount Wilson observations is nearfy up to date. 

 An investigation of the periodicity of solar radiation is under way 

 and is about to yield interesting results. A periodicity attending the 

 period of the sun's rotation is found in 1915 when there was much 

 sun-spot activity. 



A determination of the constant of the formula for total radiation 

 is in progress. 



Langlcy Aerodynamical Laboratory. — In the report of the secre- 

 tary of the board at its meeting on December 14, 1916, a brief state- 

 ment was made on the development that had taken place in connection 

 with the Langley Aerodynamical Laboratory. 



In this statement attention was called to an allotment of $2,500 

 for the investigation of problems of the atmosphere in relation to 

 aeronautics in cooperation with the United States Weather Bureau of 

 the Department of Agriculture. Through the representations of the 

 National Advisory Committee for Aeronautics, Congress appropri- 

 ated $100,000 for work in this important field by the Weather Bureau, 

 and the $2,500 allotted by the Institution have been credited back into 

 the fund of the Langley Aerodynamical Laboratory. 



The work of the National Advisory Committee for Aeronautics 

 has enlarged rapidly during the past year. At its suggestion the 

 Council of National Defense appointed a Committee on Aircraft Pro- 

 duction, which was later reconstituted under an act of Congress 

 the Aircraft Board, with power to consider all questions of aircraft 

 production and to make recommendations to the military departments 

 for the production and purchase of aircraft and aircraft appliances. 



