These are places where a whisper, or other low sound, may be heard from one part to another, to a great distance. They depend on a principle, that the voice, etc. being applied to one end of an arch, easily passes by repeated reflections to the other.

Hence sound is conveyed from one side of a whispering gallery to the opposite one, without being perceived by those who stand in the middle. The form of a whispering-gallery is that of a segment of a sphere, or the like arched figure. All the contrivance in whispering-places is, that near the person who whispers there may be a smooth wall, arched either cylindrically or elliptically. A circular arch will do, but not so well.

The most considerable whispering-places in England are, the whispering-gallery in the dome of St. Paul's, London, where the ticking of a watch may be heard from side to side, and a very easy whisper be sent all round the dome. The famous whispering-place in Gloucester Cathedral, is no other than a gallery above the east end of the choir, leading from one side thereof to the other. It consists of five angles and six sides; the middlemost of which is a naked window, yet two whisperers hear each other at the distance of twenty-five yards.

In the Philosophical Transactions for 1746, there is a letter inserted from Robert Southwell, Esq. in which he gives the following account of some extraordinary whispering-places and echoes. - "The best whispering-plaee in England," he observes, "I ever saw, was that at Gloucester: but in Italy, in the way to Naples, two days from Rome, I saw, in a inn, a room with a square vault, where a whisper could be easily heard at the opposite corner, but not at all in the side corner that was near to you.

"I saw another, in the way from Paris to Lyons, in the porch of a common inn, which had a round vault: but neither of these was comparable to that of Gloucester; only the difference between these last two was, that to the latter, by holding your mouth to the side of the wall, several could hear you on the other side; the voice being more diffused: but to the former, it being a square room, and you whispering in the corner, it was only audible in the opposite corner, and not to any distance from thence, as to distinction of words. And this property was common to each corner of the room.

"As to Echoes, there is one at Brussels that answers fifteen times: but when at Milan, I went two miles from thence to a nobleman's palace, to notice one still more extraordinary. The building is of some length in the front, and has two wings projecting forward; so that it wants only one side of an oblong figure. About one hundred paces before the house, there runs a small brook, and that very slowly; over which you pass from the house into the garden. We carried some pistols with us, and, firing one of them, I heard fifty-six reiterations of the noise. The first twenty were with some distinction; but then, as the noise seemed to fly away, and the answers were at a great distance, the repetition was so doubled, that you could hardly count them all, seeming as if the principal sound was saluted in its passage by reports on this and that side at the same time. Some of our company reckoned above sixty reiterations, when a louder pistol was discharged."

Some persons tell us, that the sound of one musical instrument in this place will seem like a great number of instruments playing together in concert. This echo is of the multiple or tautological kind, returning one sound several times successively, so as to make one clap of the hands seem like many,- one ha, like a laughter, - or one instrument like several of the same kind, imitating each other; and by placing certain echoing bodies in such a manner, that any note played should be returned in thirds, fifths, and eighths, a musical room may be so contrived, that not only one vielin played therein shall seem many of the same sort and size, but even a concert of different instruments. Those echoes which return the voice but once are called single; whereof some are tonical, only repeating when modulated into some particular musical tone. Others, that repeat many syllables or words, are termed polysyllabical; of which kind is the fine echo in Woodstock Park, which Dr. Plott assures us will return seventeen sylla bles distinctly in the day-time, and in the night twenty. Barthius likewise, in his notes on Statius's Thebais, mentions an echo near Bingeni in Germany, which would repeat words seventeen times, as he himself had proved; and what is very strange in this echo, the person who speaks is scarcely heard at all, but the repetition most clearly, and always in surprising varieties, the echo seeming sometimes to approach nearer, and sometimes to retire to a greater distance. Vitruvius tells us, that in several parts of Greece and it ly there were brazen vessels artfully ranged under the seats of the theatres, to render the sound of the actors' voices me clear, and make a kind of echo; by which means, of th prodigious number of persons present, every one might hear with ease and plea sure.