The horn that these composers called for in their scores was the hunting-horn to which crooks had been added to enable the performer to play in different keys—pitch. The horn in its natural, or simple, form was used until 1830. After that valves, or pistons, were added and the instrument was known as the chromatic horn.
Played with a mute (con sordino) made of cloth, the horn produces a dreamy effect. Walter Damrosch makes a poetic use of the horn, so muffled, in his opera, Cyrano.
The horn as we see it to-day consists of a tube bent into a spiral (for convenience of holding), comparatively narrow near the mouthpiece and gradually widening out towards the bell. It might, therefore, be described as a conical pipe. The air-stream blown in by the player runs all through the tube vibrating as it goes all through the coils and emptying out of the bell. There are no holes pierced in it anywhere. The horn has no reed. The lips of the performer have to do all the work.
By changing the pressure of the lips on the mouthpiece the performer can cut up the vibrations into shorter lengths (just as the finger of the player on a violin shortens the vibration of the string) and thus he is able to get the harmonics of the scale.
The “crooks” are moveable pieces of tubing. They are inserted into the coils to alter the pitch. There are “crooks” for all keys.
The natural, or open, tones of the horn are not produced by means of keys that close, or open, the finger-holes, like the clarinet, or oboe. They depend first on the length of the tube—the longer the tube, the deeper the tone. The length is varied by means of “crooks.” Secondly, they depend on the muscles of the lips and the increased pressure of breath—the greater the tension, the higher the tone.
This method of producing notes is called “over-blowing.” Thirdly, upon the valves, which, when pressed by the fingers, produce notes of lower and higher pitch.
The right hand of the player is always in the bell of his instrument to prevent harsh and loud sounds and to give the tone a smooth and veiled quality.
To play the horn bouché means to stop the horn with hand, or fist. To force its tone produces a loud, brassy and even wild effect.
Now the cor à piston, or French horn, is merely the horn that we have just been describing with the “crooks” permanently attached. The performer passes from one key to another by pressing his finger on one, two, or all three pistons. The French horn F is the one most frequently used. It has a complete chromatic scale of three octaves and six notes. The mouthpiece is a funnel-shaped tube of brass, or silver, ending in a rounded ring of metal for the convenience of the lips. The cavity is cone-shaped downward, and not cup-shaped; and it is supposed that this shape has something to do with the tone.