A New Acoustical Phenomenon

Abstract

THE phenomenon described by Dr. Erskine-Murray in a letter under the above heading in NATURE of June 16 (p. 490) is particularly well heard when one is standing near a cliff or rock-face and listening to the sound of a waterfall or of the waves breaking on the seashore. The phenomenon is, of course, familiar to physicists, but it may not be so well known that use can be, and indeed often is, made of this effect in avoiding obstacles when one is walking in the dark. No doubt blind men, consciously or unconsciously, use it in this way; and it must have been so used from remotest antiquity by man and any other animals which happened to have the necessary discriminating power in hearing.