Whispering gallery to the walls, an effect that was discovered in the whispering gallery of St Paul's Cathedral in London. The extent to which the sound travels at St Paul's can also be judged by clapping in the gallery, which produces four echoes. Other historical examples are the Gol Gumbaz mausoleum in Bijapur and the Echo Wall of the Temple of Heaven in Beijing. A hemispherical enclosure will also guide whispering gallery waves. The waves carry the words so that others will be able to hear them from the opposite side of the gallery. The gallery may also be in the form
Whispering-gallery wave of organ pipes. The sound forms patterns called modes, as shown in the diagram. Many other monuments have been shown to exhibit whispering-gallery waves, such as the Gol Gumbaz in Bijapur and the Temple of Heaven in Beijing. In the strict definition of whispering-gallery waves, they cannot exist when the guiding surface becomes straight. Mathematically this corresponds to the limit of an infinite radius of curvature. Whispering-gallery waves are guided by the effect of the wall curvature. Optical whispering-gallery mode can be implemented in making high precision optical sensors. For example, they can be used in the form of hollow