REPORT OF THE SEORE'J'AKY 81 



total of all wave lengths. It also appeared plainly that the chief 

 source of error remaining ii) the determinations arises from uncer- 

 tainty of the exact effect of absorption in the great infrared water- 

 vapor bands, occurring in a spectral region where solar variation is 

 almost nil. 



These considerations led the Director to devise a method whereby 

 with a few additional observations using special glass absorbing 

 screens determinations of solar variation could be restricted to the 

 spectral region of the green, blue, violet, and ultraviolet ra^^s. 

 Apparatus for such determinations ^^as prepared at our Washington 

 instrument shop and has been installed at all three of the field sta- 

 tions. It has been in regular use at all of them since about July 

 1941 in addition to the ordinary observing. 



It also appeared that certain types of sky conditions tended to 

 produce unsatisfactory results by our present usual methods of 

 observing the solar constant of radiation. It seemed possible that 

 if in addition to our usual measurements we should observe the 

 degree of polarization prevailing in sky light a correction of value 

 might be discovered and applied in our daily measurements. Ac- 

 cordingly three copies of a sky polarization device invented by the late 

 Prof. E. C. Pickering have been prepared at our Washington instru- 

 ment shop. One is already installed at Montezuma, Chile, and has 

 been used regularly since March 1942. Such instruments will soon 

 be in use at our other stations. 



Considerable special confidential work for military purposes has 

 been done at our Washington instrument shop under the care of the 

 Director. 



The Assistant Director, Mr. L. B. Aldrich, has devoted a good 

 deal of time as a member of the Smithsonian War Committee. 



FIELD WORK 



Three solar radiation observing stations have been operated on 

 all favorable days at Table Mountain, Calif., Burro Mountain, N. 

 Mex. (called the Tyrone station), and at Montezuma, Chile. The 

 meteorological conditions have been rather less favorable than usual 

 at all three stations, but still solar-constant observations were made 

 on a majority of days at all stations. 



New reinforced concrete dwelling quarters for the director's fam- 

 ily at Montezuma were completed under field director Freeman's 

 direction and finished shortly before he was relieved by A. F. Moore 

 in July 1941, and in May 1942 the assistant's quarters were rebuilt 

 to a considerable extent. 



Improvements were also made at Table Mountain and Tyrone 

 stations. A new water supply was installed at the former, and the 

 drainage of the observing tunnel was perfected at the latter. 



