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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    stereophotochromoscope proper—in which the photographs are submittted to inspection. For a reason to be given immediately, three stereoscopic pairs of photographs of the one coloured object are taken by a single exposiu-e on one sensitive plate. Thus there are six negatives in pairs (each pair being some- times called a stereogram ) : positives of these are then made in the usual way by developing and printing upon glass ; the set of transparencies being then known as a chromogram ; for, as will presently be explained, these photographs are records of colour-effects. As the paired photographs are not to be all examined in one plane in the photochromoscope, the three pieces of glass, each with its double transparency, are hinged together by a flexible material to permit of chromatic illumination in three different planes. The essence of the Young-Helmholtz theory of colour-vision is that in the retina we must suppose three sets of end-organs, of such constitution that one set responds most energetically to light at the red-end of the spectrum, less so to greenish light, and least of all to violet; that the second set are most irritable in green light, less so in light at the extremities of the spectrum, while the third set is most susceptible in violet light, less so in greenish, least of all in reddish hght. The sensation of white light is produced when all the three end-organs are excited in nearly equal degrees. Now, it is known that it is not only pure spectrum-red rays that excite the fimdamental sensation of red (consequent upon stimulation of what we have called the first set of retinal nerve-endings), but that the red -sensation is produced by all the spectrum-rays from red to green, though most powerfully by the orange; simila.rly, the green -sensation is produced not only by spectriun-green, but by the simultaneous action of orange, yellow, yellow-green, green and green-blue (all of which rays act with varying energy on the so-called second set of nerve- endings) ; and lastly, the violet-sensation is the result of the simultaneous action of the several rays, from the green-blue to the violet extremity of the spectrum. Thus, although it is true that the three primary colours are red, green, and