KIMBALL AND MILLER. - SOLAR RADIATION 



413 



about 0.02 calories when the sun is at zenith distance 60°, and the 

 air mass = 2. 



The excess can only be attributed in part to difference in atmos- 

 pheric pressure at the two stations, since their respective averages, 

 29 inches of the barometer at Madison and 30 inches at Washing- 

 ton, would account for a difference of only about 1 per cent in the 

 atmospheric transmission coefficients for the two stations, or to 

 a difference of about 0.05 or 0.06 calories in the radiation inten- 

 sities when the air mass = 2. 



TABLE II 



Monthly Means of Solar Radiation Intensities at Washington, D. C, for 

 the Five Years May, 1905, to April, 1910, Inclusive, Expressed in Gram- 

 Calories per Minute per Square Centimeter of Normal Surface. 



T [a.m. 



January < 



(p.m. 



„ , . /a.m. 



February < 



\p.m. 



March ( a - m \ 



(p.m. 



, .. /a.m. 



April < 



(p.m. 



May ( a - m - 



(p.m. 



T /a.m. 



June < 



(p.m. 



July ( a - m - 



(p.m. 



. /a.m. 



August < 



(p.m. 



September . . . < 



(p.m. 



October < 



(p.m. 



November.. < 



(p.m. 



December. . . . < 



(p.m. 



AIR MASS 



1.0 



1.41 



1.39 

 1.41 

 1.26 



1.26 

 1.35 



1.24 



1.5 



1.38 

 1.20 

 1.32 

 1.19 

 1.20 

 1.17 

 1.16 



08 

 21 

 01 

 08 

 04 

 30 

 19 

 26 

 1.23 

 1.44 

 1.45 



2.0 



1.20 

 1.24 

 1.29 

 1.23 



1.14 

 1.08 

 1.05 

 1.13 

 1.01 



1.06 

 1.15 

 0.90 



0.95 



1.19 

 1.05 

 1.15 

 1.14 

 1.29 

 1 22 

 1.21 

 1.24 



2.5 



1.05 

 1.12 

 1.16 

 1.12 



1.04 

 1.02 

 0.95 

 0.99 

 0.87 



0.99 

 1.03 



1.05 

 1.01 

 1.06 

 1.03 

 1.20 

 1.11 

 1.15 

 1.14 



3.0 3.5 



1.05 

 1.04 

 1.10 

 1.01 



1.01 



1.00 



0.88 



0.88 

 0.95 



0.95 

 0.95 

 0.93 

 0.93 

 1.11 

 1.02 

 1.07 

 1.05 



0.94 



0.95 



0.91 



0.85 



0.84 

 0.91 

 0.92 

 1.01 

 0.97 



4.0 



0.88 



0.93 



0.82 



0.81 



0.84 

 0.97 

 0.89 



4.5 



0.83 



0.83 



5.0 



0.76 



0.74 



0.82 



0.88 



0.65 

 0.79 

 0.77 



Note: — The air mass is approximately the secant of the sun's zenith distance. 



