The Probert Encyclopaedia of Music

TRUMPET

The trumpet is a musical instrument of the brass family. The trumpet is the earliest known brass wind instrument, and consists of a tube of about 1.5 meters long curved twice to form three lengths for convenience of holding. One end widens into a bell and the other end is mounted with a cupped mouthpiece. The pitch of notes is altered by way of key operated valves.

Originally a trumpet could only produce the notes in the harmonic series of the key in which it was pitched, necessitating the use by the player of different crooks whereby the length of the tube could be altered.

These crooks gave the keys of F, E, E flat, and D, all of which sounded higher than the notation of C in which the part was written. With the C crook, the notation and the crook were in unison; with the B flat crook, the sound was a tone lower. Even with the crooks, however, there were inevitable lacunae in the scale. The first notable attempt to remedy this defect consisted of an adaptation of the slide principle, like a trombone, by which the pitch could be altered for a semi-tine or a tone without change of crook. The modern trumpet, however, is fitted with valves so that any note can be obtained within the compass.
Research Trumpet