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MARCI 20, 1885.J THE PHOTOGRAPHIC NEWS. 179 To avoid fogging the plates, it would be sufficient to submit to the action of a phosphorescent plate covered with yellow glass for about three or four seconds. This light will have the effect of disturbing the equilibrium, and pre-disposes the plate to submit more quickly to the action of reflected rays. With a view to this object, I have the idea of a special dark slide allowing this feeble exposure before the actual one. The inner surface of the moving slide is coated with sulphide of calcium, over which is a sheet of yellow gelatine. A thin movable slide covers over this surface, which is opened and shut to expose the plate to the phosphorescent surface, and both slides open together for the exposure to the object. By this means the sensi tiveness is increased by One-fourth. There are some curious experiments to try on this track. Pdlevin Suhscriptions—The amount subscribed to the Poitevin monument is highly satisfactory, and exceeds the expectations of the promoters, amounting altogether to 10,500 francs. The Photographic Society of Vienna has just contributed 483 francs. Photo-Tupographic Blocks.— MM. Deroulde and Terpereau showed before the Photographic Society of France photo-typographic blocks obtained by a counter mould from gelatine with a metallic composition, having the property of taking up the fatty ink in certain parts, and leaving it in others without previous wetting. The results shown leave much still to be desired, but they are the pre liminary trials capable of opening up the way to something more complete. The mould is formed by an amalgam which hardens as soon as it has taken the impression from the gelatine, and its molecular nature is such, that with the help of mercury, which destroys the homogenous property of the metal (zine probably) with which it is amalgamated, some of its particles retain the ink, and others leave it. Leon Vidal. THE RETINA OF SCIENCE. BY DR. T. CHARTERS WHITE. The photographic camera has been compared to the eye, and in the essential elements of its construction it bears a somewhat close analogy to the the organ of vision, Thus in the eye we have the iris acting as a stop in front of the crystalline lens, which in its turn throws the image on the retina as on a focussing screen, or a sensitive plate in the camera. A French savant once not inaptly styled the sensitive photographic plate the “ retina of science,” but a reference to the accompanying Dallastint will show that the sensitive film possesses some power of discriminating greater than that possessed by the human retina, as structure quite invisible under the microscope has become distinctly so in the photographic negative. It was with no little astonishment now two years ago that I saw this result after taking a photo-micrograph of some young tench in their eggs. I well remember the clear structure less character of these jelly-like envelopes enclosing their restless inmates, and also the undesirable movements by which they manifested their objection to the “ fierce light " of my lamp beating on their dwellings. I quieted these movements by the addition of a weak solution of iodine green to the water in the trough which held my prisoners, and ultimately succeeded in taking their portraits as above. When I developed the negatives—for I took more than one—I was much astonished to find that what was clear and gelatinoid under the microscope, was now pierced by innumerable tubes which passed through the egg cases in parallel lines, and proving that the retina of science possesses a power which the human retina does not, a phenomenon which has yet to be explained by future investigation. The second Dallastint accompanying this short article INTERNAL SURFACE OF INFANT’S CUTICLE. serves to show the capabilities of that process in the de lineation of photo-micrographic subjects. We have here the internal surface of the cuticle of an infant, in which the delicate reticulated structure of the stratum mucosum is well displayed ; while scattered about may be seen the pouch-like terminations of the hair follicles, and the open ings of the sudoriparous glands.
