Nature . photographs werereadily obtained upon a moving plate, in which thesalient features of the images described by Koenig wereclearly brought out. The gas was subsequently enrichedby passing it through a receiver of petroleum ether, andin this way the brilliancy of the flame was further greatlyincreased. In Merritts experiments the moving platewas shot horizontally through the field of the camera ata speed sufficient to separate properly the various flame-images. The speed of the plate-holder, which wasarranged to slide between guides, was about two metresper second. The entire time-period
Nature . photographs werereadily obtained upon a moving plate, in which thesalient features of the images described by Koenig wereclearly brought out. The gas was subsequently enrichedby passing it through a receiver of petroleum ether, andin this way the brilliancy of the flame was further greatlyincreased. In Merritts experiments the moving platewas shot horizontally through the field of the camera ata speed sufficient to separate properly the various flame-images. The speed of the plate-holder, which wasarranged to slide between guides, was about two metresper second. The entire time-period covered by thechrono-photographs thus produced was only a fewhundredths of a second. Chrono-photographs of the manometric flame havesince been made by Hallock and Muckey {The LookerOn, 1896, pp. 1,177 and 375, 1896), who used such flames,excited by resonators, in the analysis of the voices ofvarious opera singers ; by the writer in collaborationwith Prof. Mertln {P/tysical Review, yo\. vii. p. 93, 1897),. and by Miss J. A. Holmes {T/iesis~m manuscript-Library of Cornell University, 1898). Acetylene gas, which has come into common use sincethe experiments just described were made, affords a lightof much greater actinic power than any which wasformerly available. The flame of burning magnesiumalone surpasses that of acetylene in brilliancy. Thecarbon bands in the electric arc, to be sure, give thatsource of light, likewise higher actinic value than theacetylene fiame ; but the arc light cannot be usedmanometrically, nor, indeed, is it probable that themagnesium flame could be thus employed. When we surround the acetylene flame with pureoxygen in a burner, like that described by Prof. Merritt,its actinic power is still further increased. In 1897 the writer spent many pleasant hours of thesummer vacation with Prof Merritt in the fascinatingwork of photographing the manometric flame. Thee<perinients of 1893 were repeated with acetylene inpace of ordinary enriched burning gas, an
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