"Years ago," he said, "even before that wonderful Frenchman, Daguerre, invented light photography, scientists were trying to discover some means of mechanically registering on paper, the beautiful things they saw in nature, in their natural colours, as well as in their natural form in black and white. All through the years of the development of photography with light and shadow, scientists never relaxed their search for some way of photographing colours. Although many of them hit upon the colour screen idea by which it finally was accomplished, there remained years and years of patient experiment. Prof. James Clark Maxwell, Ducos du Hauron, Doctor Konig, Sanger Shepherd, and, in later years, Frederick Eugene Ives, of Philadelphia, all worked on the idea. "In 1907, however, Antoine Lumiére, of the famous French photographic house that bears his name, announced a system of colour photography which has grown in popularity ever since. The system, which is known as the autochrome, was the result of many years patient study and research with his sons who are associated in business with him." The scientist then went on to explain that in attacking the problem the investigators first had to learn all they could about colours, and how they are reflected by light rays. As we have seen in the colour process for motion pictures there are really only three fundamental or primary colours, and all other shades and tints are made up from combinations of these. The three are blue-violet, green, and orange-red, and a screen of these forms the foundation of all the colour plates now used. In the autochrome process the lowly potato, which we generally think of merely as a common article of our food, forms the first factor. The starch of the potato is ground down and sifted so that the grains are the same size--not more than 0.0004 to 0.0005 of an inch in diameter. These grains then are divided into three equal portions, and each portion is dyed, respectively, blue-violet, green, and orange-red. The three little piles of starch grains are then mixed together in suitable amounts and dusted on to a plate, which has previously been coated with a substance to make them stick. The difficulty in dusting on the starch grains is great, for they must cover the whole plate equally and yet not make any piles of starch at any one point, for to have several grains on top of one another would spoil the effect. The extreme delicacy of this operation will be appreciated when it is realized that there are over five million grains to the square inch. When the starch is all properly placed it makes the colour screen, though in appearance the plate is a dark gray.