a mountain nymph, employed by Jupiter to baffle and mislead Juno, while he himself sported with her sister Oreades among the glades of Boeotia. As soon as Juno discovered the deception, she punished the nymph by changing her into an echo. In this condition she became enamoured of Narcissus; and when that youth failed to return her love, she pined away, till at length nothing remained of her but her voice.

from ἦχος a sound, or rather from ἦχος an echo. Sounds are reflected from the surfaces of hard bodies, such as hills, rocks, walls, &c., in such a manner that the angle of reflection is equal to the angle of incidence; and, in certain circumstances, these reflexions produce very remarkable echoes. The form of the reflecting surface, plane, or convex, or concave, &c., modifies the reflection. Sounds are also reflected by the surface of water, and sometimes even by clouds. In an elliptical room, if the sound proceed from one of the foci of the ellipse, a person placed in the opposite focus will hear the sound much more distinctly than if placed in any other part of the room. The phenomena of whispering domes and whispering galleries depend on similar principles,—for example, in the case of the dome of St Paul's Cathedral, London. Some echoes repeat only sounds of a certain pitch. Others are said to repeat sounds, but not at the same pitch as the original sounds. Such is the echo at Rosencath in Scotland, which is said to repeat a musical sound three times, but each time lower and lower by the interval of a tone. There seems to be some error in this observation at Rosencath. An echo at Genetay, six miles from Rouen, is said to repeat words several times in varied tones. Other echoes, called polyglottal, repeat many syllables or words. Multiple or taustological echoes repeat the same word several times; as at the castle of Simonetta, about two miles from Milan, where the echo repeats a word about twenty times over. Another, near Coblentz, is said to repeat a word seventeen times. Gasendi mentions an echo near the tomb of Cecilia Metella at Rome, which repeated the first verse of the Æneid eight times. Dr Plot, in his Natural History of Oxfordshire, mentions a remarkable echo at Woodstock Park, near Oxford, which repeats seventeen syllables in the daytime, and twenty at night. Another echo, on the north side of Shipley Church, in Sussex, is said by Harris (Lex. Tech.) to repeat distinctly, in favourable circumstances, twenty-one syllables.

Echo is also used for the place where the repetition of the sound is produced or heard. In echoes, the place where the speaker stands is called the phonic centre, and the object or place that returns the voice the phonoeumptic centre.

Music, is a term applied to that sort of airs or pieces in which certain passages are repeated with diminished intensity of sound. Paisiello, in his Proserpina, and Mayer, in his Elisa, employed this kind of echo. Skilful performers on the horn, the flute, the clarinet, &c., produce echo passages with great effect. A certain organ stop is also called an echo; and on the same instrument an echo is imitated by means of alternate loud and soft stops,—the latter repeating phrases given out by the former. (q.v.)

Architecture, a term applied to a certain kind of vault or arch, made commonly of an elliptic or parabolic figure, for the purpose of producing artificial echoes.