Captain Abney, in a recent address before a section of the British Association ~, made some brief remarks upon the subject of heliochromy, which are, in my opinion, so misleading as to call for correction. I quote as follows:
"The nearest approach to success in producing colored pictures by light alone is the method of taking three negatires of the same subject through different colored glasses, complementary to the three color-sensations, which together give to the eye the sensation of white light. The method is open to objection on account of the impure color of the glasses used. If a device could be adopted whereby ortly those three parts of the spectrum could be severally used which form the color-sensations, the method would be more perfect than it is at present. Even then. perfection could not be attained, owing to a defect which is inherent in photography. This defect is the imperfect representation of gradation in tone."
According to those recent text-books on color which I have seen, only such light rays as are supposed to affect only one kind of nerve fibrils in the eye, or to excite only one of the fundamental color-sensations, can be said to form or represent primary color-sensations, and such rays are confined to bott/ends and a narrow strip in the middle of the visible spectrum, t If Captain Abney means to assert that in a process of this character only those rays of the spectrum should act, which represent primary color-sensations, he is certainly mistaken, and grievously misleading all those who accept him as an authority upon this subject.