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    Édouard Eugène Désiré Branly. Autograph Letter Signed.
    "Edouard Branly." Two pages (of a bifolium), in French, on Laboratoire de Physique (located at the Institut Catholique de Paris) stationary, 5.5" x 8.5", [Paris]; February 15, 1913. In a letter addressed to "Madame," Branly informs his unnamed correspondent that "the author of the experiments you are interested in M. Dussaud [François Dussaud (1870-1953) a Swiss physicist and inventor, known for his work in the field of sound recording.] has published multiple variants of his essays and I have just written him to inquire about his conclusions. In the meantime I would like to point out his procedures appear to be aimed at facilitating cinematographic viewings or photographic projections without respect to the specific type of illumination. He therefore increases the intensity of his incandescent bulbs and by a thoughtful use of optics, avoids the extravagant loss of light one finds with typical arc lights. Also, I do not think he can refer to his lighting as 'cold light' since light produced by incandescence cannot be cold, having been produced by an excess of heat. Some incandescence can be cooler than others but all are still hot. Only the light of the glow-worm and the light of tubes filled with a noble gas can be said to be cold. I hope to be able to provide you with more details shortly."
    Édouard Eugène Désiré Branly (1844-1940) was a French inventor, physicist, and professor at the Institut Catholique de Paris. He is primarily known for his early involvement in wireless telegraphy and his invention of the Branly coherer, a radio signal detector used in the first radio receivers, around 1890.
    Condition: Except for a light horizontal fold and an impression left by as paper clip, the letter is in very good condition.

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