<P> It is said that Daguerre has found the means to collect, on a plate prepared by him, the image produced by the camera obscura, in such a way that a portrait, a landscape, or any view, projected upon this plate by the ordinary camera obscura, leaves an imprint in light and shade there, and thus presents the most perfect of all drawings...a preparation put over this image preserves it for an indefinite time...the physical sciences have perhaps never presented a marvel comparable to this one . </P> <P> A further clue to fixing the date of invention of the process is that when the Paris correspondent of the London periodical The Athenaeum reported the public announcement of the daguerreotype in 1839, he mentioned that the daguerreotypes now being produced were considerably better than the ones he had seen "four years earlier". </P> <P> At a joint meeting of the French Academy of Sciences and the Académie des Beaux - Arts held at the Institut de Françe on Monday, 19 August 1839. François Arago briefly referred to the earlier process that Niépce had developed and Daguerre had helped to improve without mentioning them by name (the heliograph and the physautotype) in rather disparaging terms stressing their inconvenience and disadvantages such as that exposures were so long as eight hours that required a full day's exposure during which time the sun had moved across the sky removing all trace of halftones or modelling in round objects, and the photographic layer was apt to peel off in patches, while praising the daguerreotype in glowing terms . Overlooking Nicéphore Niépce's contribution in this way led Niépce's son, Isidore to resent his father being ignored as having been the first to capture the image produced in a camera by chemical means, and Isidore wrote a pamphlet in defence of his father's reputation Histoire de la decouverte improprement nommé daguerréotype (History of the discovery improperly named the daguerreotype with a note on its real inventor Joseph Nicéphore Niépce </P> <P> Daguerre was present, but complained of a sore throat . Later that year William Fox Talbot announced his silver chloride "sensitive paper" process . </P>

Who discovered that iodized silver plates could produce direct positive images