SOLAR RADIATION 



215 



winter and summer solstices, or - 11° 44' on February 18 and October 24, 

 and +11° 44' on April 21 and August 22. Note first of all the marked 

 minimum noon intensity at Sante Fe in August, which is also seen to a 

 lesser degree at the other stations, and is only exceeded in some other 

 month of the year at Madison, Wis., the most northern station, in Decem- 

 ber. While this August depression is partly due to the greater solar 

 distance of the earth at that season, it is principally due to the increased 

 water vapor and dust content of the atmosphere in late summer. At 

 Davos, Switzerland [(6), Table 1], farther north than any station in the 

 United States, and with a low humidity content of the atmosphere, there 

 is a noon minimum in July, and a decided maximum in April, with a 

 secondary maximum in August. The absolute minimum here also occurs 

 in December, as we would expect. 



Just before sunset or immediately after sunrise, if the sky is clear, the 

 radiation received on a surface normal to the rays is still strong. Meas- 

 urements made at Washington, D. C. (7), on November 9, 1909, give the 



o 



following intensities, on the Angstrom scale : 



T.\BLE 2. — Radiation Intensity with Sun Approaching Horizon 



T.ABLE 3. — Coordinates of Stations Recording the Total (Direct + Diffuse) 

 Radiation Received on a Horizontal Surface, and Type of Pyrheliometer 



Employed 



Stations 



Miami, Fla 



New Orleans, La . . 

 Riverside, Calif . . . 



Fresno, Calif 



Washington, D. C 



Pittsburgh, Pa 



New York, N. Y.. 



Lincoln, Neb 



Chicago, 111 



Blue Hill, Mass... 

 Twin Falls, Idaho . 

 Madison, Wis. . . . 

 Fairbanks, Alaska 



Lati- 

 tude 



25 41N. 

 29 56 N. 

 33 58 N. 

 36 43 N. 

 38 56 N. 

 40 32 N. 

 40 46 N. 

 40 50 N. 

 4137N. 

 42 13 N. 



42 29 N. 



43 06 N. 

 64 52 N. 



Longi- 

 tude 



80 12 W. 



90 07 W. 

 117 20 W. 

 119 49 W. 



77 05 W. 



80 20 W. 



73 58 W. 



96 41 W. 



87 35 W. 



71 07 W. 

 114 25 W. 



89 23 W. 

 147 39 W. 



Alti- 

 tude, 

 ft. 



100 

 1070 



330 



397 

 1114 



156 

 1225 



688 



635 

 4300 

 1009 



500 



Period of time 



Nov. '29-Aug. '34. 

 Mar. '31-Aug. '34. 

 June '33-Aug. '34. 

 Oct. '28-Aug. '34. 

 Oct. '14- Aug. '34. 

 Dec. '29-Aug. '34. 

 Apr. '24-Aug. '34. 

 July '15-Aug. '34. 

 Sept. '23-Aug. '34. 

 Dec. '32-Aug. '34. 

 June '26-Aug. '34. 

 Apr. '11-Aug. '34. 

 Aug. '31-July '34. 



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