An integrating photometer

Abstract

The paper is a description of a type of integrating photometer designed to measure the total amount of light arriving at a point on the earth's surface, from the sun and sky, irrespective of the position of the sun or of the distribution of cloud. Some measurements made with it, shewing the variation of direct sunlight and of indirect sunlight (arriving from clouds, &c.) throughout a typical day, are given as an illustration of its use.