HORNS, TRUMPETS, AND CORNETS
THE wood-wind group of instruments derive their tone from the vibration of reeds, even the flute being considered to have an air- reed, or space of compressed air near the blow-hole acting like a reed. In the brass instruments there is no such device. The player presses his lips against a brass mouthpiece, and blows through a narrow opening between them. If his lips are loose, no tone will result; but if he stiffens them, they vibrate regularly, and transmit their vibrations to the air column in the tube. By increasing the stiffness of the lips, the player can make them vibrate more quickly, and cause the air-column to subdivide, giving overtones. While only a few such overtones are used in the wood-wind group (obtained by increased force of blowing), a much larger number of overtones can be produced on the brass instruments. In the socalled natural instruments, such as the bugle or the Waldhorn (forest horn), these overtones (harmonies) are the only notes that can be obtained. On the valve instruments there are valves (keys) which act by throwing in extra sections of tubing and lowering the pitch. Still other brass instruments, such as the trombone and slide trumpet, are made with inner and outer tubes, so that the length of tube used can be altered by pulling or pushing, as with a telescope. The mouthpiece of the brass instruments is a metal cup, or cone, against which the lips are pressed.
The simplest brass instrument is the natural horn, or Waldhorn. This is merely a tube with a mouthpiece. Horns of this sort have been known from ancient times. They were much used for military signals, and in the middle ages for hunting calls. The simplest horn of to-day, the post-horn, consists of a mouthpiece and a straight tube. The hunting-horn was bent in a single curve at first, and later on in a threefold circle, so that it could be hung on the shoulder. Louis XV, with his master of the hunt, systematized the horn-calls, giving a meaning to each, and making some of them quite intricate.