Sound / by John Tyndall.

  • Tyndall, John, 1820-1893.
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: Sound / by John Tyndall. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    its furniture. The presence of an audience may also ren- der intelligible speech possible where, without an audience, the definition of the direct voice is destroyed by its echoes. On the 16th of May, 1865, having to lecture in the Senate House of the University of Cambridge, I first made some experiments as to the loudness of voice necessary to fill the room, and was dismayed to find that a friend placed at a distant part of the hall could not follow me because of the echoes. The assembled audience, however, so broke up and quenched the sonorous waves, that the echoes were practically absent, and my voice was plainly heard in all parts of the Senate House. Sounds are also said to be reflected from the clouds. Arago reports that when the sky is clear the report of a cannon on an open plain is short and sharp, while a cloud is sufficient to produce an echo like the rolling of distant thunder. The subject of aerial echoes will be subsequently treated at length, when it will be shown that Arago's con- clusion requires correction. Sir John Herschel, in his excellent article ' Sound' in the ' Encyclopaedia Metropolitana,' has collected amoDg others the following instances of echoes. An echo in Woodstock Park repeats seventeen syllables by.day and twenty by night; one on the banks of the Lago del Lupo, above the fall of Terni, repeats fifteen. The tick of a watch may be heard from one end of the abbey church of St. Albans to the other. In Gloucester Cathedral, a gallery of an octagonal form conveys a whisper seventy- five feet across the nave. In the whispering gallery of St, Paul's, the faintest sound is conveyed from one side to the other of the dome, but is not heard at any inter- mediate point, At Carisbrook Castle, in the Isle of Wight, is a well 210 feet deep and 12 wide. The interior is lined with smooth plaster; when a pin is dropped into the well it is distinctly heard to strike the water. Shout-