Valved brass instrument .
It evolved in the 1820s from the posthorn. Like the trumpet , it has three valves, but its bore is somewhat more conical. It is a transposing instrument (its music written a tone above the actual sound), usually built in the key of B-flat, though a higher-pitched E-flat instrument is used as well. Its range parallels that of the trumpet. Its agility made it a very popular solo instrument; it often displaced the trumpet in 19th-century orchestras, and it preceded the trumpet in modern dance and jazz bands. Recent developments have made the two instruments very similar, and the cornet's popularity has waned considerably as a result.