revolving scenes, which were called versatiles. The wo of 
Pollux were the same thing. This author, in treating of the 
parts of the theatre, says that the t dered, or the scene on the 
left hand, sometimes represented a house of mean appearance; 
at other times a ruined temple; and sometimes was without 
any device of this kind, according to the subject of the piece 
represented. It would be absurd to suppose that the changes 
of the scene were effected by different paintings upon the 
doors of the permanent scene. 
We now come to the consideration of a practice mentioned 
by our author, upon the subject of which no research has 
hitherto thrown any light. This was the disposing of 
brazen vases below the seats of the spectators in order to 
assist the powers of the voice. It is a matter of doubt 
whether the practice to which he alludes was ever resorted 
to; and whether the mention he makes of it might not have 
been prompted by the desire of reducing all practice under 
the guidance of physical principles which, as we have before 
observed, manifests itself in various parts of his work. The 
idea might have been suggested by an observation of 
Aristotle' upon the efficacy of hollow vessels in causing 
the vibration of sounds, and extending their effects, when 
covered and buried. 
There is a passage in Pliny which alludes to a mode of 
building peculiar to the walls of theatres: for in constructing 
the walls of other edifices, the interior space between the 
two faces of the wall was filled in with rubble; whereas in 
theatres, hollow vessels of earthenware were immured: and 
1 Prob. 8 and 9, Sect. II.