A powerful brass instrument of the trumpet kind, thought
   by some to be the ancient sackbut, consisting of a tube in three parts,
   bent twice upon itself and ending in a bell. The middle part, bent
   double, slips into the outer parts, as in a telescope, so that by
   change of the vibrating length any tone within the compass of the
   instrument (which may be bass or tenor or alto or even, in rare
   instances, soprano) is commanded. It is the only member of the family
   of wind instruments whose scale, both diatonic and chromatic, is
   complete without the aid of keys or pistons, and which can slide from
   note to note as smoothly as the human voice or a violin. Softly blown,
   it has a rich and mellow sound, which becomes harsh and blatant when
   the tones are forced; used with discretion, its effect is often solemn
   and majestic.