One writer, a singer, speaks of living in the same house with two deaf-mutes.

He lodged on the first floor, they on the third.

One day, meeting at luncheon, one of the deaf-mutes told the singer that he had begun practice earlier that morning than usual.

Surprised, the writer asked how he knew.

The deaf-mute replied that they always knew when he was singing because they felt the floor of their room vibrate.
If tone vibrations can be transmitted so readily throughout a house, it is not difficult to understand how easily the vibrations of bone and tissue can be transmitted until the whole framework of the body responds in perceptible vibration.
It is said that Pascal at the age of twelve wrote a dissertation on acoustics suggested by his childish discovery that when a metal dish was struck by a knife the resulting sound could be stopped by touching the vibrating dish with a finger.
With this in mind it is not difficult to understand how compression of the human instrument by the pressure of tight clothing without, or by false muscular tension within, must interfere with its free vibration and so rob the produced tone of just so much of perfection.
From these experiments we can understand that, while the tones of the voice are initiated by or at the vocal cords, the volume and character of the tones are dependent upon _resonance_,--the vibration of the air in the various resonance chambers of the body, together with the sympathetic vibration of the walls of these chambers and the bony framework that supports them.
In respect to resonance, as in other respects, the human voice is far superior to all other instruments, for their resonators are fixed and unchanging, while the human resonator is flexible,--in Helmholtz's words "admits of much variety of form, so that many more qualities of tone can be thus produced than on any instrument of artificial construction." We are now prepared to realize the error of the common notion that loudness of tone is due entirely to increase of breath pressure on the vocal cords.