Grove's dictionary of music and musicians

462 SINGING SINGING
Besides the tension of the membranes there
is another physical condition which undergoes
variation with every change of pitch, and that
is the air-pressure exerted by the breath.
From experiments (M'Kendriok, Schdfer's
Physiology) it is found that the air-pressure
varies in about the same ratio as the tension.
Therefore, in a general plan of the vocal compass
the middle note may be regarded as the
product of both mean tension and mean airpressure.
The tension is well known to vary
in the ratio of the square of the vibrations, and
thus both the tension and air-pressure may be
represented by the numbers 1, 4, 9, 16, 25,
while the vibrations are as 1, 2, 3, 4, 5, in the
diagram appended.
Pressure and
Tension.
Vibrations.