Biot's paper and Arago's plates. Photographic practice and the transparency of representation

François Arago and Jean-Baptiste Biot, two of the physicists most involved in early photography, mobilized this new technology for their ongoing debates about the proper boundaries of the public in France. Each threw his weight behind one of the competing photographic processes, Arago supporting daguerrian silver plates and Biot favoring paper soaked in silver solution. For both men, disagreement at the level of materials and techniques was further bound up with disagreement about what kind of visual evidence the photograph was and who was capable of understanding it. Biot argued for a severely restricted community of photographic practitioners. His papers, he claimed, revealed an invisible world of chemical radiation accessible only to those who understood the chemistry involved. Arago's reliance on resemblance, on the other hand, permitted him to present daguerreotype plates as a form of representation available to all, even incorporating them into his campaign for universal male suffrage.