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220 and Z in the case of the plain developer, and by C TS and E in the case of the developer with thio-sina- I S mine, the black letters representing deposit, and the light ones freedom from it. Similar results were obtained with bromide paper and gelatine dry plate films, but it may be remarked that, whereas the C plates showed with both developers a clear image of the varnished C, surrounded by more or less dense deposit (much denser and yellower with the thio- sinamine), there was a marked difference in the Z plates, that immersed in the plain developer showing a dense deposit with a clear Z, while, with the thio-sinamine developer, the Z is shown dark on a clear ground. Ferrous oxalate does not seem to give such marked reversals—at any rate with bromide paper—as eikonogen does, and this agrees with the photographic results. With gelatine dry plate silver bromide films, it was noticed that, in the ferrous oxalate developer, the Z plates darkened first, and with the thio-carbamide the C plates blackened first and most strongly. The developers seem to be good conductors of the electric current, and do not increase the resistance very much. It may also be noted that pencil marks made at the back of the papers were found to be reproduced very strongly on their film side, in contact with the silver plates, and were strongest on plates treated with the thio-sinamine developer. Having obtained these results with bromised silver plates, a further trial was made with similar plates to see if a current could be detected between an unexposed and an exposed plate without the aid of the battery, and this time with a more successful result. The plates were, as before, treated with bromine water, washed, and dried. The developer used was made up of 1 part each of eikono gen and carbonate of lithia, and 2 parts of sodium sulphite, in 100 parts of water. One plate having been exposed to a weak yellowish light, the plates were attached to the poles of the galvanometer, and the unexposed plate immersed in the developer. On dipping the exposed plate, the needle at once deflected some ten degrees, but quickly returned to zero. Another pair of plates gave the same result. A third pair immersed in the same way in some of the same developer, to which thio-sinamine and potassium bromide had been added in the proportions given above, showed a similar deflection, but the needle remained for some time at about five degrees, and only very slowly returned to zero. It may be noted that after fixing, the exposed plate of this last experiment showed a black deposit with a dark line at the immersion edge. It showed little or no tarnish, and, C in most respects, corresponded with the TS plates of the experiments with the battery. The under-exposed plate, on the other hand, showed a very considerable yellow tarnish, stronger on the back of the plate than on its face, and no marked line at the immersion edge. Generally it corresponded with the re plates 13 of the battery experi ¬ ments with the thio-sinamine developer. The two plates used with the plain developer showed very little difference. There was deposit on both, but the exposed plate showed a light line at the immersion edge, and the unexposed one showed a black line. On repeating the experiment, but with the plates attached to the wooden block, so that they were immersed together, it was found that, with the plain developer, no distinct current was produced on immersing the plates, or afterwards, though there seemed to be very faint indica tions of a current, which might be visible with a more delicate galvanometer. With the thio-sinamine developer, however, although there was no immediate deflection, the needle slowly turned in the same direction as before, to about five degrees, remaining there for some time, and then again slowly returning to zero. This action seems to correspond with the gradual change of the photographic image under the thio-carbamide developers. On repeating this experiment with a fresh pair of plates, in fresh developer containing only one per cent, of sodium sulphite, and about 5 drops to the ounce of an alcoholic solution of Professor Reynolds’ compound salt of thio carbamide and ammonium bromide, exactly the same result was obtained. The strong initial deflection of the needle when the plates were immersed separately appears to be due to polarity, and was noticed by Becquerel. On immersing two unexposed plates in the same way in plain developer, the same deflection was noticed, and very much stronger. These results cannot be taken as conclusive, and a great deal of farther investigation is necessary with other deve lopers and thio-carbamides, as well as with other silver haloid films, used with and without the silver-plate con ductors. The products formed at both poles by the electrolytic decomposition have also to be examined. As far as the experiments go, however, they seem to show: (1) That the same kind of reversal of the deposit can be effected by a developer containing thio-sinamine, both electrically and photographically; (2) that the re versal of the photographic image on bromide of silver films by thio-carbamides is, to a great extent, if not entirely, due to electro-chemical action ; (3) that the development of the photographic image on silver bromide is accompanied by electrical action. Taken in connection with Professor Minchin’s recent observations, and the earlier ones by Becquerel and others, they appear to point to the conclusion that photographic action, at any rate as regards the haloid salts of silver, is influenced by electricity, both in the action of light upon the silver haloid film, as well as in the development of the invisible image so produced, to a very much larger extent than has usually been recognised. This aspect of the theory of photography appears to have been somewhat neglected, but it seems likely that farther investigation in this direction would be rewarded with valuable results, and throw some further light on the mystery which still surrounds the formation and development of the invisible photographic image. Putney Amateur Photographic Society.— Six new members were elected at the meeting on the 28th of February, when there was an exhibition of lantern slides. Photographic Society of Great Britain.—March 24th, technical meeting ; subject for discussion, “ Hand-Cameras ” ; members are requested to bring their cameras with them. March 31st, lantern evening, and discussion on lantern matters. April 14 th, Mr. W. Willis will read a paper on “ Platinotype." April 28th, subject for discussion, “Animal Photography.” The exhibition of collotypes will remain open till April 14 th.
