A description is given of the construction and performance of a portable ultra- violet intensity meter, consisting of a photoelectric cell (of titanium, uranium, cadmium, etc.), a balanced amplifier circuit, and a comparatively insensitive microammeter.A means is described for testing the constancy of the sensitivity of the amplifier.It is found that, after preliminary operation for 5 to 10 minutes, to attain tem- perature equilibrium in the amplifier tubes, there is no fluctuation in the zero scale reading of the microammeter either when testing the amplification sensi- tivity of the instrument, or when making measurements of ultraviolet intensities, of the sun and of artificial sources, by means of the photoelectric cell.The indicator response (scale reading) was found linear within the accuracy of the microammeter used.Owing to the selective wave length response of the photoelectric cell, this de- vice, like all selective radiometers, is calibrated in absolute value, by means of the standard balanced thermopile and filter radiometer (" differential actinometer") described in RP370 and RP450.
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Coblentz et al. (1934) studied this question.
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