Supplementary to an earlier paper in the Review of Scientific Instruments for August, 1940, this paper gives additional technical data on the construction and a discussion of important applications of a Wheatstone bridge type of balanced direct-current photoelectric amplifier adapted for use on 110-volt a-c commercial power lines. This instrument is especially adapted for use with the standard recorders now employed by the U. S. Weather Bureau in the study of Solar radiation. The determination of the amount and variation of ozone in the stratosphere, and of the total intensity of ultraviolet solar radiation in a definite wave band, are discussed as the important applications of the instrument. Performance tests indicate that the instrument is equivalent to the older battery type in sensitivity and precision. It is, furthermore, free from the disadvantages of requiring frequent voltage adjustments, sensitivity tests, and the continual attention of an experienced operator.

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