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SOME EARLY APPLICATIONS OF PHOTOGRAPHY 219
bad purpose, for indecent photographs have been thus placed in the hands of unsuspecting persons — a fact that speedily brought this branch of photography into discredit. But there are circumstances in which such microscopic photographs can be of extraordinary value. Simpson in England called attention to the fact that, by the help of photography, the contents of whole folios can be concentrated within a few square inches, and that the substance of books filling entire halls, when reduced by microscopic photography, can be brought within the compass of a single drawer — a circumstance which, with the enormous increase of material that has to be stored by our libraries, may be of importance. Of course, either a microscope or a magic lantern, would be required to read such microscopic works.
Microscopic photographs have obtained great importance in promoting pigeon despatches. During the siege of Paris, in 1870, the blockaded city held communication with the world outside by means of balloons and carrier pigeons. The first mode of communication was used almost exclusively for political objects ; the second only admitted the transmission of very light letters. Letters, however condensed, could scarcely have been sent more than two or three at a time by a pigeon. In this case, microscopic photography presented a valuable means of concentrating many pages on a collodion film of only one square inch, and so light that more than a dozen packed in a quill could be sent by one pigeon. Dagron, at Paris, who first prepared microscopic photographs, also was the first to prepare these pigeon despatches. All the correspondence which had to be diminished was first set up in type, and printed together on a folio page. A microscopic photograph was made of this folio page, contained in about the space of 1J square inches. The collodion film of the picture was then removed from the glass by pouring a collodion over it which contained