Colour Measurement

Abstract

MR. GUILD'S letter¹ makes it clear that the recent conflict in views on colour measurement arises by his adopting an interpretation of the role of the C. I. E. colorimetric system which puts it outside purely physical discussion. The explanation he suggests does not, however, apply, as I have not been concerned with the public and practical aspect to which he refers. As was clearly stated², my remarks referred to the purely physical analysis of the phenomenon of colour, and measurement of the quantities following from such analysis: the C. I. E. system was therein referred to for what fundamentally, apart from all implication and interpretation, it actually is, namely, a conventional schematization of physical fact, having reference to certain conditions of observation, based, of course, upon averaged data but nevertheless representative in such conditions of a possible real observer (of. the analogous purpose served by Listing's typical schematic eye in ophthalmology). In this sense the system forms in general a representative first-order theory. Such use of the system accords with normal physical practice, for no suggestion of compromise in form, or simplification of the phenomenon has hitherto been implied in the reduction of physical data to refer to the C. I. E. normal observer.