The French Horn
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Horns made of shells, wood and animal horns have been used for signaling for centuries. The European orchestral horn, the french horn, is a gradually tapered metal tube roughly 10 feet long coiled in concentric circles. It gets its name either from the close-coiled helical horn used by Cavalli and Lully in the late 17th century, or the more elegant and slender trompe, with two half coils, used for hunting in France and later Bohemia. The french horn used in the 18th- and 19th-century orchestras had “crooks,” a series of removeable tubes which allowed it to play in different keys. Today this instrument is known as the “natural” horn.
Modern horns have three or four valves, which also act to lengthen or shorten the basic length of tubing, providing a full chromatic scale (all the white and black keys of the piano).
Horn players can produce “stopped” or dampened notes by placing the fist inside the bell. Mutes produce a more distant sound effect, such as the bleating of a flock of sheep in Strauss’ Don Quixote.
Source: The Norton/Grove Concise Encyclopedia of Music, edited by Stanley Sadie. London: Macmillan Press Ltd.,  ISBN 0-333-43236-3