| Unidentified photographer Ducom's photographic apparatus 1908 (published) Book illustration Internet Archive LL/53291 Alfred Hildebrandt, 1908, Airships past and present, together with chapters on the use of balloons in connection with meteorology, photography and the carrier pigeon, (London, A. Constable & Co. Ltd.), p. 304, fig. 188
Originally published in Pizzighelli's, (1881), Handbook for Photography.
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