XII. The Bakerian Lecture.—Colour photometry

Abstract

We think it may possibly be of some interest to the Royal Society if we lay before them the account of the method which we have used, and the results of some experiments which we have made, in measuring the relative illuminating intensities of different parts of the spectrum, as seen by ourselves and by others, and those of different parts of spectra produced under varying circumstances, more particularly as these results have considerable bearing on practical photometry. In the Phil. Mag. (ser. 5, vol. 20 (1885), p. 172), one of us described a method which he had previously demonstrated to the Physical Society of forming patches of monochromatic light upon a white screen, and alluded to the possibility of adapting it to researches on colour. The method, briefly described, is to pass light through a spectroscope, using a photographic camera in place of the observing telescope, then to isolate different portions of the spectrum and make them fall in a patch on a white screen by means of a lens as shown in fig. 1. Any variations in the apparatus are described further on.