Abstract
ONE form of an optical sonometer recently made by Messrs. Adam Hilger, Ltd. (of 75A Camden Road, N.W.i), is shown diagrammatically in Fig. 1. The Fig. 1, apparatus is designed to record the pressure variation caused by sound waves. It consists of a diaphragm: box B, to which is attached a horn for receiving sound waves. In box B is a diaphragm with a platinised, silvered, or gilt inner face; this is the actual receiver. Recording the vibrations produced in the disc is accomplished by means of a beam of light directed from the source D (a Pointolite Lamp of 30 or 100 candle-power) by a condenser E through the slit F and brought to a focus on the diaphragm C. Thence by means of lenses G and H an image of the slit is formed on the photographic paper or film on the drum J. The lens H being cylindrical with its axis parallel to the drum, the beam of light is brought to an intense point image on the drum, and as the latter rotates a record of the deflection of the diaphragm is obtained. The spot of light can be focussed on the drum at any distance from 4 to 20 inches according to the amplitude of vibration under investigation and the degree of magnification consequently required.
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An Optical Sonometer. Nature 110, 464 (1922). https://doi.org/10.1038/110464a0
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DOI: https://doi.org/10.1038/110464a0