ECHI'NUS. the "egg and tongue" or " egg and anchor" ornament, frequently met with in classical architecture, carved on the ovolo. The type of this ornament is considered to be derived from the chest nut and shell.
EMU°, a sound reflected or reverber ated from some hard surface, and thence returned or repeated to the ear. As the undulatory motion of the air, which con stitutes sound, is propagated in all direc tions from the body, it will fre quently happen that the air, in perform ing its will impinge against various objects, which will reflect it back, and so cause new vibrations the contrary way ; now if the objects are so situated as to reflect a sufficient number of vibra tions back, viz., such as proceed different ways, to the same place. the second will be there repented, tun is called an cello; and the greater the distance of the object is, the longer will be the time before the repetition is heard : and when the sound, in its progress, meets with objects at dif ferent distances, Eufficient to produce an echo, the same sound will be repeated several times successively, according to the different distanedi of these objectA from the sounding body, which inakoo what is called a repeated echo. Echoes are not, however, caused by a mere re pulsion of the sonorous particles of air, fur then every hard substances would pro duce an echo ; but it is supposed to re quire a certain degree of concavity in the repelling holy, which collects several oh verging lines of sound, and concentrates them in the place where the echo is audi ble, or, at least, reflects them in parallel lines, without weakening the sound, as a concave mirror collects in a focus the di verging rays of light, or sometimes sends them back parallel. The celebrated echo
at Woodstock, in Oxfordshire, repeats the same sound fifty times. But the most singular echo is that near Rosneath, few miles from Glasgow. If a person placed at a proper distance from this echo plays eight or ten notes of a tune with a trumpet, they are correctly repeated by the echo, but a. third lower ; after a short pause, another repetition is heard, in a lower tone ; and then, after another in terval, a third repetition follows in a still lower tone.—Echo, in architecture, any vault or arch constructed so as to produce an artificial echo. These are generally of a parabolic or elliptic form ; of this kind is the whispering-gallery in St. Paul's cathedral.—Echo, in poetry, a sort of verse which returns the sound of the last syllable, the elegance of which con sists in giving a new sense to the last words.