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THE PHOTOGRAPHIC NEWS. EDITED by T- c. HEPWORTH, F.C.S Vol. XXXV. No. 1720.—August 21, 1891. CONTENTS. PAGE Photography in Starland 585 Photography in France. By Leon Vidal 586 Developing. By E. Decker 587 The Zoologist’s Debt to Photography. By G. A. B 588 Practical Directions for the Retouching of Positives. By A. Chevalier 500 Photographic Exhibition in Glasgow 591 International Photographic Exhibition at Cardiff. By Our Special Commissioner 593 PAGE Notes 592 Meeting of the British Association at Cardiff 595 The Decomposition of Silver Chloride by Light. By A. Richardson 59G Lunar and Terrestrial Volcanoes... 597 Patent Intelligence 599 Correspondence 599 Proceedings of Societies 599 Answers to Correspondents 909 PHOTOGRAPHY IN STARLAND. As might be expected, Dr. Huggins, in his presidential address to the British Association assembled at Cardiff, devoted a great deal of attention to the important work which has been done, and which is yet in progress, in which the photographic plate is being employed for the portraiture of the heavens. He called to mind the noteworthy circumstance that, at the very beginning of the history of photography, on the occasion of the announcement of the discovery of Niepce and Daguerre to the French Academy by Arago, that savant held out the hope that the wondrous new method of picture making would be applicable to a more perfect delineation of the sun and of the moon than had before been dreamt of, and we all know that the prophecy came true, for such pictures were among the first which were success fully accomplished by the new art. These pictures, in fact, are still pleasant to look upon, so well are they executed, in spite of the many disadvantages under which they were produced, and with which photographic processes at that time were necessarily associated. Even after the wet collodion method came into vogue, the difficulties of photography, although lessened, had not by any means been removed, and astronomical photography—except so far as it related to picturing the orbs of day and night—was still unheard of. And this, as the president of the British Association was careful to point out, was not for lack of instruments, but simply because of the shortcomings of the chemical process employed. The young photographer of to-day, why buys his plates ready prepared for his camera, has little notion of the anxiety and trouble which practice of the art involved under the old order of things. It would be beneficial to him in other ways, as it certainly would be as an item of photographic education, were he to learn in a practical manner how to clean a glass plate, how to collodionise it, and how to prepare a silver bath in which to sensitise it. He would soon see that the workers of old had many difficulties to cope with of which before he was ignorant, and possibly he would, after this experience, be the more ready to acknowledge the debt which he owes to the pioneer workers, and to the makers of commercial dry plates. If a candid man, he might even go so far as to acknow ledge that, if photography were still to involve all the worry and mess that it was once credited with, he would never have bothered himself with a camera and its belongings. The modern astronomer is in much the same position as the hypothetical being whose position we have just reviewed. He, too, can say that if photography still involved the use of a wet plate he would have none of it, not for the reason of its troublesomeness, but simply because it was not adapted to his work. For the sun and moon the old process was, as we have seen, good enough, for the flood of light given forth by the former was sufficient to impress a plate with its image in a very small fraction of a second, while the reflected light of the latter afforded sufficient radiance to perform the work in less than a minute; but when the more remote bodies in space came to be considered, it was found that their light was insufficient to impress the plate while the latter remained in a sensitive state. The collodion surface broke down, or rather, it became insensitive as the moisture evaporated from it, and therefore it required to be used fresh from the bath, or not at all. It is true that, by certain treatment with honey, &e., the evaporation could be delayed for a long time, but still not long enough to suit the purpose of the astronomer. Then came the sudden revelation that, in the gelatine dry plate, we had a new agent which could do things which never had been accomplished before; a plate which was so sensitive to feeble rays of light that the utmost precautions had to be taken in all the necessary manipulations. The old brilliant yellow light, in which the photographer was wont to work, had to be discarded in favour of a deep red, which seemed just enough to make darkness visible. But beyond their wondrous sensitiveness, the new plates had other merits of an equally noteworthy kind. The chief of these was that they preserved their properties for an almost indefinite time, and development of the image could be