The measurements of solar radiation intensity at normal incidence made at Washington, D. C., Madison, Wis., Lincoln, Nebr., and Santa Fe, N. Mex., have been utilized in determinations of the intensities for the Atlantic Coast States, the Plains States, and the Rocky Mountain plateau, at latitudes 30°, 36°, 43°, and 48° N., at hourly intervals on the 21st day of each month. Corresponding determinations of the intensity of the radiation received on a horizontal surface, and of the total radiation per day, have been made from the vertical component of the normal intensities, and measurements by the Callendar recording pyrheliometer of the diffuse radiation received on a horizontal surface from the sky. The variations in the daily totals with altitude and with cloudiness have also been determined.
From the relation between the total solar or heat radiation and the visible or luminous radiation, determined by means of synchronous pyrheliometric and photometric measurements made at Mount Weather, Va., in 1913–14, the solar radiation intensities at normal incidence above described have been converted into illumination intensities at normal incidence, and on vertical surfaces facing S., SW., W., NW., N., NE., E., and SE. Also, the total illumination on a horizontal surface from the sun and sky has been determined for clear sky and completely overcast sky conditions.
Most of the remits are shown in both tables and charts, the latter consisting of isopleths of heat or of luminous solar radiation, with hour angles of the sun as ordinates and days of the successive months as abscissas, except that the daily totals of radiation on a horizontal surface on the 21st of each month are shown by means of radiation isograms on outline maps of the United States.
The effect of surface slope on solar radiation intensities is briefly considered.