Solar Variation and the Weather

Abstract

NEARLY a century ago three pioneers, Sir John Herschel, Pouillet, and Forbes, laid the foundations of the measurement of solar radiation. Each devised an instrument for measuring the heating effect of the solar rays and used it diligently. Pouillet and Forbes availed themselves of the law of extinction of light, which had been independently discovered about 1760 by Bouguer and Lambert, to calculate the intensity of the solar rays, as they would be outside our atmosphere. Forbes's researches in the Alps proved that this law is not strictly applicable to the sun's rays as a whole, and he was led to believe that the value of the so-called solar constant of radiation was as high as 2.85 calories per sq. cm. per mm. Pouillet's value, based on the assumed validity of the Bouguer-Lambert law, was 1.76 calories.