The new international standards, which define a standard observer, three standard illuminants, standard conditions of illuminating and viewing opaque specimens, a standard for evaluating the brightness factor of opaque specimens, and a standard trichromatic system for the expression of colour measurements, are stated and their origin explained. In addition to the numerical tables which are appended to the resolutions setting up these standards, there are given a table specifying the trichromatic coordinates for the standard observer of all spectral colours at wave-length intervals of 1 mμ, tables to facilitate the calculation of the standard coordinates and the brightness factor of a material illuminated by any one of the three standard illuminants from spectrophotometric measurements on the material, and a table giving the coordinates of some stimuli of special importance on the N.P.L. system, the standard system, and another system which occurs in the resolutions. Some new colorimetric terms are proposed, partly to avoid misinterpretation and partly to meet new needs. The theory of colour transformations, and points which arise in the application of the system and in the calibration of instruments, are discussed.
W D Wright 1929 Trans. Opt. Soc. 30 141
Using a new trichromatic colorimeter a series of colour matches through the spectrum has been made by ten observers. The results have been averaged and a mean set of trichromatic coefficients for the spectral colours derived. These results are compared with previous determinations made by König and Abney. The variations in the coefficients that have been found amongst the ten observers must, as a consequence of a new method of basing the trichromatic units, be attributed to variations in the process of reception, but their magnitude appears to be of a small order. On the other hand, there are big differences in the amount of the macular pigment in different eyes and probably some variation in its dominant hue. These variations have been investigated by matches on a standard white, results for 36 observers being given in the paper and a mean value determined. This value, combined with the mean spectral coefficients, has been used to compute an average locus for the spectral colours in the colour triangle, with white at the centre.
Other points discussed in the paper include the technique of colour matching, the range of intensity over which matches remained valid, and variations of luminosity.
F Twyman and A Harvey 1931 Trans. Opt. Soc. 33 1
A direct experimental test is made of the Schwarzschild relation as applied to the logarithmic sector used in conjunction with a quartz spectrograph. The relation is found to hold within the limits of the experiment, from which it follows that the length of a spectral line on the photographic plate is proportional to the logarithm of its intensity.
F Twyman 1931 Trans. Opt. Soc. 33 9
The design and construction of the "Spekker" photometer are described, special attention being paid to certain pitfalls of spectrophotometry which have been avoided in this instrument.
F Campbell Smith and Ensor R Holiday 1931 Trans. Opt. Soc. 33 20
The photometer described makes use of a device by means of which absorption measurements may be made in the ultra-violet region of the spectrum without recourse to calibrated wedges or sectors. The hydrogen discharge tube is used as the source of radiation. A photo-electric bridge is employed, one arm of which is controlled by a small fraction of the light falling on a third cell; the current from the latter may be measured galvanometrically. The two fractions are kept in constant proportion over the range of intensities used.
W. Watson & Sons, Ltd. 1931 Trans. Opt. Soc. 33 29