A method is described for comparing the candlepower of carbon lamps with that of tungsten lamps which avoids the usual difficulties of heterochromatic photometry. The method is based on photometric comparisons of carbon lamps with a black body immersed in freezing platinum and of gas-filled tungsten lamps with a black body immersed in freezing iridium. The relative integral brightness of the two black bodies is calculated from the ratio of brightness measured at one wave length with an optical pyrometer.
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Wensel et al. (1934) studied this question.