4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



termination depending basically on observing from mountain tops 

 can claim with certainty to be within 1 percent of the absolute scale 

 of heat. But as will be shown below, a series such as ours, where 

 every effort was made to retain a constant scale over many years, 

 can be depended on to preserve its relative homogeneity to 1/6 of 

 1 percent in daily values, even though 1 or 2 percent away from the 

 true absolute scale throughout. 



Volleys of criticisms of our solar-constant determinations were 

 published between 1910 and 1914 by numerous authors. These we 

 answered by several papers, but as they still continued we published 

 (P. 2361) the extensive paper "New Evidence on the Intensity of 

 Solar Radiation Outside the Atmosphere." This has three distinct 

 parts : 



(1) On September 20 and 21, 1914, two of the clearest and most 

 uniform days ever experienced on Mount Wilson, we observed for 

 the solar constant continuously from sunrise to 10 o'clock. This 

 yielded for both days, by Langley's spectrobolometric method, solar- 

 constant values computed as between air masses 1 .3 and 4.0 ; 4.0 and 

 12.0; 1.3 and 20.0. All these six solar-constant measures (Langley's 

 method) fell between 1.90 and 1.95, which shows both the excellence 

 of the sky conditions and the accuracy of the observing. 



(2) At Dr. A. K. Angstrom's suggestion I designed, and our 

 instrumentmaker Andrew Kramer constructed, five copies of an auto- 

 matic combined pyrheliometer and barometer. These were flown 

 by balloons from Omaha by L. B. Aldrich, with the cooperation of 

 Dr. William R. Blair and his assistants from the U. S. Weather 

 Bureau, on July 11, 1914. One instrument was recovered uninjured 

 in Iowa. It was caUbrated both before and after flight under the same 

 conditions of temperature and barometric pressure that obtained dur- 

 ing flight. It rose to 24,000 meters, where 24/25 of the atmosphere 

 lay below. It yielded a value of 1.87 calories, a value that lies within 

 the limits of solar variation, as observed in those times at Mount 

 Wilson, and as expressed on the Smithsonian "scale of 1913." 



(3) Here I quote the concluding paragraphs of our paper: 



It seems to us that, with the complete accord now reached between solar 

 constant values obtained by the spectro-bolometric method of Langley, applied 

 nearly 1,000 times in 12 years, at four stations ranging from sea level to 

 4,420 meters, and from the Pacific Ocean to the Sahara Desert; with air- 

 masses ranging from 1.1 to 20; with atmospheric humidity ranging from 

 0.6 to 22.6 millimeters of precipitable water; with temperatures ranging from 

 0° to 30° C. ; with sky transparency ranging from the glorious dark blue above 



