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United States National Academy of Sciences

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    Abstract

    THE half-yearly meeting of the National Academy of Sciences was held at Philadelphia, Nov. 2, 3, and 4, 1875. Prof. Joseph Henry has for several years been conducting the researches of the U.S. Lighthouse Board in respect to Fog Signals and the Transmission of Sound. While these experiments are not yet completed, the results up to the present time give the following indications:—The echo of sound passing over the ocean is more probably due to reflection from the surface of the waves than from the air; sound coming against the wind can certainly be heard at an elevation from a greater distance than at the sea level; with the velocity of the wind at about five miles an hour, sound was heard five times further with the wind than against it; sound is heard furthest with a moderate wind; with a strong wind it is not heard so far as in still air.

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