SOLAR RADIATION 225 



zenith distance of the sun is less than 60° only from about May 15 to the 

 end of July. At Mount Evans, Greenland, and at Abisko, Sweden, 

 the solar-zenith distance is at 60° or less from about April 15 to the end of 

 August. Table 6 shows that at Treurenberg with zenith distance 

 60°, m = 2, the solar-radiation intensities average 1.30, 1.32, and 

 1.36 gm. cal./min./cm.2 f^j. May, June, and July, respectively; for 

 Mount Evans for April, August, and September, the intensities are 

 1.45, 1.22, and 1.32, respectively, and for Abisko for July and August, 

 1.17 and 1.16, respectively. 



For stations in the United States for which radiation intensities are 

 summarized in Table 1, the Weather Bureau file gives for average summer 

 intensities for m = 2, the following values: at Blue Hill, 1.08; for Wash- 

 ington, 0.94; Madison, 1.02; Lincoln, 1.10; Santa Fe, 1.27. For Samoa 

 the corresponding intensity is 0.98. 



If we reduce the intensities measured at Arctic stations with the sun 

 60° from the zenith to mean distance of the earth from the sun, we 

 obtained the following transmission coefficients: Treurenberg, May to 

 July, 0.718, which Fig. 1 shows to be about the same as for Mount Wilson 

 in September; Abisko, July to September, 0.541, which is close to that for 

 Lincoln in August; Mount Evans in April, and in August and September, 

 respectively, 0.753 and 0.665, the first of which is about the same as that 

 for Sante Fe in January, and the second close to that for Lincoln in 

 February. With the exception of that for Abisko, these are high coefla- 

 cients for the summer season. 



REFERENCES 



1. Abbot, C. G., and L. B. Aldrich. Smithsonian pyrheliometry revised. Smith- 

 sonian Misc. Coll. 60 (No. 18): 1-7. 1913. 



2. Abbot, C. G., and L. B. Aldrich. The standard scale of solar radiation. Smith- 

 sonian Misc. Coll. 92 (No. 13). 1934. 



3. Angstrom, Anders. Scientific results of the Swedish Norwegian arctic expe- 

 dition in the summer of 1931. VII. On the total radiation from sun and sky at 

 Sveanor. Geografiska Annaler 15 {%): 151-160. 1933. 



4. Angstrom, Anders, and Olaf Tryselius. Total radiation from sun and sky 

 at Abisko. Geografiska Annaler 16 (1): 53-69. 1934. 



5. Angstrom, Kntjt. The absolute determination of the radiation of heat with the 

 electric compensation pyrheliometer, and examples of the application of this 

 instrument. Astrophys. Jour. 9: 332-346. 1889. 



6. Dorno, C. Tagliche, jiihrliche und sakulare Schwankungen der Sonnenstrahlung 

 in Davos. (Rapport fait a la 1™ Conference Internationale de la Lumiere, 

 Lausanne-Leysin, 10-13 septembre, 1928.) 



7. Kimball, Herbert H. Solar radiation, atmospheric absorption, and sky- 

 light polarization, at Washington, D. C. Bull. Mt. Weather Observ. 3: 69-126. 

 1910. (See p. 92, Table 2.) 



8. Kimball, Herbert H. Measurements of solar radiation intensity, and deter- 

 minations of its depletion by the atmosphere, with bibliography of pyrheliometer 



