I. On the photometry of the magneto-electric light

Abstract

At intervals during the last three years it has been my duty to ascertain the value of the illuminating power of different sources of light, which have been brought before Government for military purposes. As there is nothing secret in the results obtained, it seemed to me that I might communicate them to the Royal Society, I have obtained permission so to do. There are certain difficulties to be overcome which affect the measurements, as it will be evident that the question of colour enters largely into them, which are not so great when lights produced by comparatively low temperatures are in question.