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pelled by an infinite number of circles similar to those 
generated in standing water when a stone is cast therein. 
which, increasing as they recede from the centre, extend 
to a great distance, if the narrowness of the place ov 
some obstruction do not prevent their spreading to the 
extremity ; for when impeded by obstructions, the first 
recoil affects all that follow. In the same manner the 
voice spreads in a circular direction. But, whereas the 
circles in water only spread horizontally, the voice, on 
the contrary, extends vertically as well as horizontally, 
Wherefore, as is the case with the motion of water, so 
with the voice, if no obstacle disturb the first undulation. 
not only the second and following one, but all of them 
will, without reverberation, reach the ears of those at 
bottom and those at top. On this account the ancient 
architects, following nature as their guide, and reflecting 
on the properties of the voice, regulated the true ascent 
of steps in a theatre, and contrived, by musical propor¬ 
tions and mathematical rules, whatever its effect might 
be on the stage (scena), to make it fall on the ears of the 
audience in a clear and agreeable manner. Since in 
brazen or horn wind instruments, by a regulation of the 
genus, their tones are rendered as clear as those of 
stringed instruments, so by the application of the lays 
of harmony, the ancients discovered a method of in 
creasing the power of the voice in a theatre. 
CHAPTER IV. 
OF HARMONY. 
HAEMONY is an obscure and difficult musical science, but 
most difficult to those who are not acquainted with the 
Greek language ; because it is necessary to use many 
Greek words to which there are none corresponding in