The whispering gallery phenomenon at St. Paul's Cathedral

Abstract

The very curious and interesting acoustical effects observed in the Whispering Gallery under the dome of St. Paul's Cathedral have, as is well known, been explained by the late Lord Rayleigh as due to the curvilinear propagation of sound, the waves which proceed from a source placed close to the wall of the gallery clinging to its surface and creeping tangentially along it. This view was developed mathematically by Lord Rayleigh ("Scientific Papers", vol. 5, p. 617), the theoretical conclusions arrived at being (a) that the sound-waves travel in a comparatively narrow belt skirting the wall, the thickness of this belt decreasing with the wave-length of the sound; (b) that in this belt the intensity is a maximum near the wall and decreases rapidly and continuously as we proceed radially away from it; and (c) that the intensity does not fluctuate markedly as we proceed circumferentially parallel to the wall.