Heterochromatic photometry of the ultra-violet region

Abstract

The advantage of greater sensitivity which the photoelectric cell possesses over the thermopile or bolometer is nullified by its selectivity when radiations of different wave-lengths are to be compared. The experiments described show that by the use of fluorescent substances in conjunction with such a cell it can be made non-selective while retaining a great advantage of sensitivity. It has been shown by Wawilow that the ratio of quanta of fluorescent light emitted to quanta of light absorbed in strong solutions of uranin and aesculin in water is independent of wave-length beyond certain thresholds. The accuracy of his measurements, however, while sufficient for the approximate demonstration of the foregoing relationship, was not enough for their use in quantitative work. Experiments were therefore made to discover the conditions under which the best results could be obtained from fluorescent substances.