There are _seven_ positions for this slide and they have to be learned. There is no guide but the performer’s ear, which has to be as accurate as that of a violinist; and, indeed, we may say that the seven positions, in a certain sense, correspond with the positions on the violin. They are only acquired by constant practice; and when they are once acquired, the performer thinks no more about them but pulls his slide up and down with an air that seems to us almost indifferent. These seven positions of the slide each give a fundamental tone and its harmonics. According to an authority: “The slide, being entirely closed, that is to say, the tube reduced to its shortest dimension, the instrument produces (modifying with the breath and the pressure of the lips as in the horn) the harmonics. By pulling out the slide a little, which increases the length of the tube, we have the second position and its harmonics.” Pulling out the tube still farther makes the third position and its harmonics; and so on. There are three varieties of this instrument: the alto, the tenor and the bass. Each is written in the proper key of the voice whose name it bears. Trombones differ from all other brasswind instruments in that they are non-transposing, and, therefore, render the notes as they are written. The compass of the instrument is two octaves and a sixth. “The _timbre_ of the trombone,” writes Lavignac, “is majestic and imposing. It is sufficiently powerful to dominate a whole Orchestra. It produces above all things the impression of power, a power superhuman. For the loudest passages there is no instrument more stately, noble, imposing; but it can also become terrible, or, even _terrific_, if the composer has so decreed; and terrific also in the softest passages. It is mournful and full of dismay. Sometimes it has the serenity of the organ. It can, also, according to the shades of meaning, become fierce, or satanic; but still with undiminished grandeur and majesty. It is a superb instrument of lofty dramatic power, which should be reserved for great occasions; when properly introduced, its effect is overwhelming.” Mozart understood this reserve. In _Don Giovanni_, for instance, he kept them out of the Orchestra until the scene with the statue. They come in, therefore, in a climax, a terrific and solemn voice from the lower regions calling Don Giovanni to his doom. Mozart also used them very impressively for the March of the priests and to accompany Sarastro, the high priest, in _The Magic Flute_. Beethoven gave the trombones much to do in the _Ninth Symphony_, where they begin in the Trio of the _Scherzo_. Schubert uses them strikingly in his _Symphony in C_; and Schumann in the Finale of his _First Symphony_ and also in his _Manfred Overture_.