_series_ of the seats at that end, which we may reasonably judge were last filled by the spectators. These noble buildings, which were of a fine invention, and well calculated for their uses, were most frequently called, from their hollow figure, _cavea_; of which there are many quotations to be had out of the old poets, and other writers: and originally it was inherent to theatres; in which sense commonly used by Cicero and others, but at length passed chiefly to amphitheatres, as the greater works. The matter of some was brick, as that near Trajecto in the Campania of Italy; another at Puteoli; others stone, and others solid marble; as that famous one at Capua, another at Athens, and that at Verona. The amphitheatre which is still in part to be seen at Pola in Istria, was of stone and wood too; for the whole frame of the seats was made of timber, the portico’s only, or external part, of stone. The wit of man could not find out a fitter scheme for commodiousness of seeing and hearing: and in some respect, I conceit, they had an eye to the form of their harps, fiddles, and such instruments of music, as modulate sounds in a roundish cavity: the oval turn thereof, and the solidity of the materials, had all the requisites of receiving and returning the vibrations of the air to greater advantage. Vitruvius advises, in this case, that the place, as well as the stuff, wherein these buildings are set, and of which they are composed, must not be what he calls _surd_, such as deaden the sound, but make smart repercussions, and in just space of time; which is of great consequence in the philosophy of echoes: for if the voice strike upon a solid that is not harmonious in its texture, that is, whose parts are not of a proper tone or tenseness, not consentaneous to the vibrations of musical notes; or if this solid be too near, or too far distant, so that it reverberates too quick, or too slow, as a room too little, or too great; all the main business of hearing and sounds is disturbed. Vitruvius is very large upon this head, to whom I refer the reader. Now I suppose the ancients learnt by experience and trial, as well as by reasoning upon the nature of things, that such a capacity and compass, and of such extent, was best for this end: whence we find, that all their amphitheatres are much about the same bulk, and executed upon nearly the same proportions. A thing of this kind deceives the eye without strict consideration; for it is bigger than it seems, and a person in the middle of it, to one upon the terrace, looks lesser than one would imagine. It is true indeed, that ours is not made of so solid materials as brick, stone or marble; but yet it is possible there may be as much an error in one extreme as the other, and nature affects a mediocrity. One shall scarce doubt that a _convallis_, or proper convexity between two mountains, will give as fine an echo as any artificial work that can be contrived. I can say, however, in favour