because no other sound in the chromatic genus can bein consonance therewith. In the upper division andrange of the cavities, the vases on the extremities areconstructed to produce the tones of the diatonic hyper-bolseon: in the next cavities, those of the diatonicdiezeugmenon, a fourth: in the third, of the diatonicsynemmenon, a fourth: in the fourth, of the diatonicmeson, a fourth: in the fifth, of the diatonic hypaton,a fourth : in the sixth, proslambanomenos, a fourth : inthe centre, mese, between which and proslambanomenosis an octave, and a fifth between it and the diatonichypaton. He who is desirous of more fully understand-ing these matters, must refer to the musical diagram atthe end of the book, which is that left to us by Aris.toxenus, who with much intelligence and labour, formeda general scale of the tones. Hence, he who carefullyattends to these rules, to the nature of the voice, and tothe taste of the audience, will easily learn the method ofdesigning theatres with the greatest perfection. Someone may perchance urge, that many theatres are yearlybuilt in Rome, without any regard to these matters. Butlet him not be herein mistaken, inasmuch as all publictheatres which are constructed of wood, have manyfloors, which are necessarily conductors of sound. Thiscircumstance may be illustrated, by consideration of thepractice of those that sing to the harp, who when theywish to produce a loud effect, turn themselves to thedoors of the scene, by the aid of which their voice isthrown out. But when theatres are constructed of solidmaterials, that is of rubble, squared stones or marble,which are not conductors of sound, it is necessary tobuild them according to the rules in question. If it beasked what theatre in Rome can be referred to as anexample of their utility, we cannot produce one, butsuch may be seen in some of the provinces of Italy, andmany in the Grecian States. We moreover know thatL. Mummius, on the destruction of the theatre at