ON A SIMPLE METHOD OF RECORDING THE TOTAL AND PARTIAL INTENSITIES OF SOLAR RADIATION

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Abstract
A simple form of recording pyrheliometer is obtained from the combination of a thermopile of the Moll type with a recording voltmeter of the Richard type. The large-surface thermopile is composed of 80 elements made from thin strips of manganin and constantan, which are placed in a circle nearly 2 cm, in diameter. These strips can be exposed to radiation over their whole length. The thermopile is question affords a high degree of stability (absence of zero errors) and sensitivity, together with great quickness in action, namely, the time elapsing between the admission of radiation and the moment at which the full electro-motive force is reached, is less than two seconds. The radiation from a candle at one meter distance yields about 90 microvolts. Other details and some historical data are given. With a recording voltmeter (Richard type) the large-surface thermopile, properly diaphragmed and equatorially mounted (clock driven), gives a new form of thermoelectric pyrheliometer, very rugged, and simple in use even for inexperienced observers. A solar radiation intensity of one gram-calory per minute per square centimeter of surface normal to the incident rays develops a current having an electromotive force of about 16 millivolts; this voltage is very nearly proportional to the intensity of the solar radiation so that the pyrheliometric records can be directly calibrated in gram-calories/cm.2/min. An illustration of the new pyreheliometer is given, with three sample records from measurements made by the author in the Desert of Sahara. The method of obtaining the partial intensities by the use of colored glasses and liquid light filters is also indicated.

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