Note on the stereophotochromoscope : a new optical instrument / by David Fraser Harris.

  • Fraser-Harris, David Fraser, 1867-1937.
Date:
[1895]
Catalogue details

Licence: Public Domain Mark

Credit: Note on the stereophotochromoscope : a new optical instrument / by David Fraser Harris. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    MR DAVID FRASER HARRIS. violet, yet this must only be taken as a succinct statement of the Young-Helmholtz theory; for while spectrum-rays of one colour will serve to re^rcmnt chromatically the corresponding fundamental colour-sensation, yet it is a physical fact that several widely-separated rays, i.e., lights of very different colours, can excite m any one normal person one and the same funda- mental sensation. We can, therefore, map out in the solar spectrum three ciu^ves, the height of each being a measure of the power of the different rays to excite their respective colour- sensations, and the area enclosed by each curve being a graphic representation of the entire group of rays, which, when simul- taneously acting, yield a particular fundamental colour-sensation. Thus any of the rays from red to yellow can excite, in varying degrees of intensity, the red-sensation, and all those rays acting together give the full fundamental sensation; but when we represent by a colour what this sensation is, we indicate it by light somewhere about the C line. And similarly for the other sensations. In fact, there is a difference between all the actual coloured rays, efficacious in producing a colour-sensation, and the chromatic representation of that fact of consciousness by a light of one definite colour. ^ The place of these rays in the spectrum, their relative sensa- tion-producing power, and their relative amount of actinic inllueuce, are physical facts ; so that, following the data given by Maxwell, Konig, and Abney, one can, to use Mr Ives' own words, by the photometric measurement of the density-curve of a spectrum negative find the relative amount of reaction by the different spectrum rays. It is therefore, he continues, onlj- necessary, in order to secure action by different rays in any definite proportions, to use such a combination of sensitive plate and colour-screen as will yield a spectrum negative having a density-curve corresponding to the graphic curve representing such proportionate action. ^ Let us call the three paired photographs or stereograms A, B, and C ; the negative of A was taken by interposing between the object and the sensitive plate a glass of such colour (yellow- orange) that only those rays capable of exciting the fundamental red-sensation acted on the plate, in the case of B the light which ' Journal of Society of Arts, May 27, 1892.