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The second part of the N.P.L.'s colour-matching investigation was devoted to determining average colour-matching properties in a large (10 ° diameter) bipartite matching field, and the final corrected results are here presented in tabular form, together with a specification of the conditions of measurement, and ancillary data on repeatability. The tabulated results comprise (a) mean colour-matching functions, referred to reference primaries at wave-numbers 15 500, 19 000 and 22 500 cm -x, for spectral stimuli in the range 12 000 to 25 500 cm -~, given at intervals of 250 cm -1 between i6 000 and 22 000 cm -1 and at intervals of 500 cm -1 outside these limits, (b) the standard deviations and correlation coefficients of the colour-matching functions at wave-numbers between 14 000 and 25 500 cm -~, (c) mean colourmatching functions corrected for rod intrusion in the range 12 000 to 17 000 cm -1, (d) the corresponding mean unit coordinates in a W.D.W. system, and their standard deviations, (e) the mean relative luminosity factors of the reference primaries and their standard deviations determined by both directcomparison and flicker heterochromatic matching, (f) the mean relative luminosity function Va in the range 12 000 to 15 000 cm -1 determined by direct comparison with 14 250 crn -1. The main colour-matching results are based on 49 subjects, but the results for spectral stimuli of wave-number less than 14 000 cm -~ rest on fewer subjects. The extent to which the results show an increase with age in the yellow pigmentation of the eye is discussed.

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The effect to be described in this paper was discovered in attempting to develop an apparatus for measuring the area of the eye pupil, using a photometric principle. The idea involved is made clear by the diagram fig. 1. The subject applies his eye to the eye-ring E and fixes his eye on the aperture in the diaphragm D. He then sees a photometric field divided into two parts. The lower half is illuminated by light diffused from the opal O, which itself receives light from the lamp S. The rays from this half of the field form a diverging beam which completely fills the pupil of the subject’s eye. The upper half of the field is illuminated by the method of Maxwellian view. An image of the small aperture P is focussed by the lens L on to the middle point of the eye-ring E. This image is only about 1.5 mm. in diameter and all the light is collected by the subject’s eye, provided the pupil of the latter is concentric with the eye-ring and has a diameter exceeding 1.5 mm. A variable graduated neutral wedge W is inserted at the aperture P and this enables the two halves of the photometric field to be adjusted to equality of brightness by the subject.

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