Sound Sensations.

Professor Bain, distinguished sound considered as sensations into three classes: The first, comprises the general effect of sound as determined by quality, intensity, and volume or quantity, to which all ears are sensitive. The second, includes musical sounds, for which a susceptibility to pitch is required. Lastly, there is the sensibility to the articulateness, distance and direction of sounds, which are the more intellectual properties. The first and principal difference between sounds experienced by the ear, is that between noises and musical tones, every variety of which depends on the rapidity, form, size, and order of succession of the vibrations. In musical tones, the vibrations are periodic, or succeed each other at regular intervals: in noises they follow each other irregularly. Musical tones begin to be perceived at about thirty vibrations in a second, but a determinate musical pitch is not perceptible till about forty vibrations a second have been reached.