NO. 3 SOLAR VARIATION AND WEATHER ABBOT 3 



is described on pages 47-52. More than 100 of these instruments have 

 been constructed, standardized, and sold at cost by the Smithsonian 

 Institution to observers in all parts of the world. For their standardi- 

 zation in absolute units, I devised the water-flow and water-stir abso- 

 lute black-body pyrheHometers (see Annals, A. P.O., vol. 3, pp. 52- 

 69). With certain improvements, the water-flow double-barreled 

 electrical-compensation pyrheliometer has been used for standardizing 

 pyrheHometers hundreds of times. It is now recognized as the world's 

 standard for measurements of solar radiation. The double-barreled 

 water-flow design was suggested by V. M. Shulgin of Russia about 

 1927 and was immediately adopted by us. 



About 1913, with F. E. Fowle and L. B. Aldrich, I did the original 

 standardizations. We used thermometers certified in Paris and elec- 

 trical instruments certified at the U. S. Bureau of Standards. Our 

 solar measures from that time to this have always been expressed "on 

 the scale of 1913." During the 40 years following, whenever im- 

 provements brought alterations we always made many checks and 

 comparisons to keep the solar constant values still "on the scale of 

 1913." Observed solar-constant values have ranged irregularly from 

 1.900 to 1,960 calories and even higher. Their mean value "on the 

 scale of 1913" is 1.944. We now recognize that the single-barrel 

 standard pyrheliometer of 1913 in our hands gave values about 2 per- 

 cent too high. This was cured by the new instrument used since 1930. 

 Various other important changes in solar-constant work have been 

 made. These include restricting the sky exposure, making larger cor- 

 rections for wavelengths beyond the violet and far in the infrared 

 not observed daily, evaluating ozone absorption, determining personal 

 equation, introduction of "the short method," and other changes. The 

 effects of all these we have applied retroactively to all the solar- 

 constant determinations from 1920 to 1955. (See Annals, A. P.O., 

 vols. 6 and 7.) Every published value was scrutinized extensively by 

 L. B. Aldrich, Mrs. A, M. Bond, and W. H. Hoover, and generally 

 by all three as a committee. So far as we have been able to bring it 

 about, the solar-constant tables in volumes 6 and 7 of Annals A. P.O., 

 and also published in my papers P. 4088 and P. 4213, form a homo- 

 geneous series, all "on the scale of 1913." 



Johnson, of the Naval Research Laboratory, using data from 

 rockets, and with critical studies and use of our work, has published 

 the solar-constant value 2.00 ±0.04 calories.^ I doubt if any de- 



3 Johnson, F. S. On the solar constant. Journ. Meteorology, vol. 11, No. 6, 

 1954. 



