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or on marshy ground, the foundations and substructure must 
be made in the manner already described for those of sacred 
edifices. Upon the substructure, the rising steps may be 
constructed either of stone or marble. The number of 
praecinctions must be proportioned to the capacity of the 
building: their height should be equal to the width of 
the passages which they form around the theatre; for were 
they made higher, the sounds would not be heard with 
distinctness by those in the seats above them; but be 
interrupted in their ascent, and reflected back from the 
upper part of the theatre. The method of arranging the 
seats is determined by extending a line from the uppermost 
to the lowest, and making the angles of all the intermediate 
steps to touch it. In theatres thus constructed the 
propagation of sound will not be interrupted. 
The approaches should be numerous and spacious; nor 
should those from the upper and lower parts of the theatre 
have any communication, but the passages to every part be 
direct, and without deviations; that when the representations 
are ended, the audience may retire with facility from all 
parts of the theatre, and not be subjected to the pressure of 
the multitude. 
We must also be careful in observing that the situation 
chosen be not calculated, through local circumstances, to 
check the dilation of sound; but, on the contrary, be such 
as to permit the free expansion of the human voice. This 
is the property of those places in which there is nothing 
to interrupt the vibrations of the air: for sound is a subtle 
fluid, acting upon the organs of hearing by the vibration of