Third Meeting: 19th July, 1904.
Professor Evans delivered an address on “Photography in Colour.”

The process in hand might, he said, be called “the reproduction of certain effects of light by means of certain other effects of light.” What, then, was light? He could not tell them. All he could say was that, just as the clearest views of the phenomena of sound were reached when we imagined them as caused by wave disturbances passing out from sonorous bodies, so was the most comprehensive understanding of the phenomena of light reached if we looked upon it as wave disturbances passing out in all directions from luminous bodies. He went on to explain the science of light, and illustrated his remarks by projecting, by means of a powerful limelight, a white light on the wall, showing that white light was made up of many other colours by inserting a prism and throwing the reflection of the visible spectrum on the wall. He then spoke at some length on the wave theory of light, and illustrated the wave-lengths by means of diagrams thrown on a screen by a lantern. The problem of colour-photography was as old as photography itself All attempts to solve it could be divided into two groups—they prepared light sensitive surfaces, which retained the colour of the light to which they were exposed, or they produced ordinary photographic pictures, which were coloured and then superposed to obtain the desired effect. The first might be called the direct, and the second the indirect method. The earliest partly successful applications were those of Becquerel, St. Victor, Seebeck, and Poiterin. The two first named covered a highly polished silver mirror with a thin layer of silver-chloride, and exposed it to the light until the delicate surface was converted to the brown subchloride. By projecting the solar spectrum on the prepared surface good coloured impressions were obtained. Poiterin substituted paper for the silver substratum, but no other substance had been found that could replace the silver-subchloride. The method and the coloured image given by that substance were not permanent; the image was destroyed by further exposure to light; and, despite numerous experiments, no chemical had been discovered that could fix the subchloride without destroying the colour. A light sensitive substance could only be altered by those coloured rays which the substance absorbed; red light would have no effect on a red body, green rays no influence on a green body. He illustrated these facts by experiments with the lights thrown on the wall, and, after exhibiting slides of photographs of various coloured flowers, showing how the different blossoms had been brought out more prominently by the use of different coloured screens in the photographic process, he went on to explain the different wave-lengths of the lights, and the impressions of photographs taken by the human eye, illustrating the latter with an optical delusion. Continuing, he said that, though the ear could distinguish the different notes in a chord, the eye did not distinguish between the colours forming one composite colour. Upon that inability most of the theories of colorisation were based. With the normal eye all the possible colour - sensations could be given