This Section
Now, the essential thing in music is the Series of Vibrations in the air. Until these are set up we can have neither the noise caused by irregular vibrations nor the musical sound caused by regular vibrations. Fortunately, almost all orchestral instruments produce musical sounds. A few, however, produce only noise. We must make our classification so as to include both these groups. It must be of the simplest possible nature, and must give us only the primary methods by which the vibrations can be mechanically set up in the air. We can then subdivide these classes by indicating either fundamental distinctions in the matter of tone-production or integral differences of shape. In more concrete language we can show, in the Strings, the various methods by which the strings* are set in motion. In the Wind, we can study the effects caused by the varying proportions of the tubes which contain the air-columns and by the different methods of tone-production.
Now all sounds, whether musical or unmusical, are merely sense-impressions caused by longitudinal air-waves* of varying shapes and sizes. These air-waves, as far as the art of orchestration goes, are set up in one of three ways:
(1) By the beating of elastic surfaces which are in contact with the air;
(2) By the regular breaking up of air-columns enclosed either in tubes of metal or in pipes of wood;
(3) By the setting in motion of stretched strings which are in contact with the air.
All orchestral instruments are included under this primary classification. We may label the three classes "Percussion," "Wind," and " Strings " respectively.
Throughout this book the words " Strings," " Brass," " Wood," are printed with a capital initial when they are used in the orchestral sense of "Stringed instruments," "Brass instruments," " Wood instruments." Without the capital letter, they have their ordinary meaning. The word " Bass," too, is used throughout with a capital in the sense of the instrument, the Double-Bass.
In air and in liquids the disturbance is always lengthwise. In solids, such as a rope, we can produce a transverse wave by means of a jerk. See " Sound," by Professor Poynting, in Encyc. Brit., xi. Ed.