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A special instrument is described in detail which has been designed in order to allow measurements of the amount of ozone in the atmosphere to be made easily and rapidly under nearly all conditions. The instrument follows the usual practice of measuring the absorption by the ozone of solar ultra-violet energy; from this measurement the amount of ozone can be deduced. A double quartz monochromator isolates certain pairs of wave-lengths, and the relative energy in the two wave-lengths of a pair is measured by allowing them to fall alternately on to a photoelectric cell, the current from which is amplified by thermionic valves. This allows great sensitivity to be obtained so that very small amounts of light can be accurately measured. For measuring the amount of ozone a pair of wave-lengths, one of which is strongly absorbed by ozone while the other is not, is selected. It is shown how the amount of ozone can still be measured when the sky is cloudy if a second pair of wave-lengths, both unabsorbed by ozone, be also measured. The results of tests which show that the accuracy is ample for meteorological requirements are given.
G. M. B. Dobson (1931) studied this question.