Ives recently explained and illustrated some improvements he has made in the means of operating the process, by which it is rendered comparatively simple and capable of immediately profitable commercial operation for lantern illustration. Ives showed that, by an improvement on his helio-chromic camera, the three negatives, representing the effect of the object photographed upon the three fundamental colour-sensations, are now not only made from one point of view by simultaneous and equal ex-posure, but also upon a single sensitive plate, so that the helio-chromic negative is obtained with no more trouble than an ordinary one, and any number can be made in which the relation of one element to the others is exactly the ' same. The colour-prints also can be made from these negatives by a single exposure in transparent gelatine, and separated only when ready to dip into the dye solutions representing the respective colour-sensations. It is not necessary to go to the trouble of making the colour prints when only lantern illustrations are required.
Lantern positives, made from the helio-chromic negatives, with no more trouble than ordinary lantern-slides, can be projected on the screen in the natural colours in the ordinary lantern by means of a special front, substituted for the ordinary projecting lens in about one second, so that an exhibition of ordinary lantern-slides can be interspersed with projections in natural colours without causing any delay in changing from one to the other. The approximation to the colours of nature is marvellously accurate. The positives are about one-third smaller than the ordinary projections; but as sharply defined, and in as bright and true colours, as those produced with the more elaborate and trpublesome lantern. The lantern front used for these new projections consists of three prisms, converging light from a single condenser and radiant to three small projecting lenses, the necessary colour screens being located just behind the objectives. Ives also has devised a camera to produce the helfo-chromic negatives, in which three negatives are made on a single plate, the image-forming rays being transmitted to the single gelatine dry plate through three reflecting prisms, and from points of view so close together (less than 1/2 in. apart) as to make perfect registration easy of accomplishment.
By another camera the three negatives are made from the same point of view.