Open AccessFog signals.―Areas of silence and greatest range of sound
Author(s) -
A. Mallock
Publication year - 1914
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1914.0103
Subject(s) - sound (geography) , silence , acoustics , range (aeronautics) , plane (geometry) , front (military) , physics , geodesy , meteorology , geology , mathematics , engineering , geometry , aerospace engineering
The experience of Trinity House in regard to the audibility of sound signals has brought to notice the fact that on occasions the sound may be heard near the source and again at a considerable distance, while inaudible between these positions. This was first observed, or at least prominently brought forward, by Prof. Tyndall. The statement was regarded with some scepticism by scientific men at the time, but the explanation of the effect of wind on sound given by Prof. G. Stokes will, with a little amplification, suffice also for the silent areas. Stokes in this explanation (which was repeated by Henry and by Osborne Reynolds) points out that the speed of the wind, in consequence of the surface friction of the ground, increases with the height, and that since the velocity of second is constant not with reference to the ground, but to the air through which the sound travels, the front of a plane wave vertical at some given instant will subsequently lean backwards if travelling against the wind, and forwards if with the wind. Or, in other words, the sound tends to leave the ground in the first case and to cling to it in the second.