An accurate acquaintance with the principles of acoustics is essential to the scientific construction of every species of musical instrument, but especially those which owe their operation to the action of the wind. Wind-instruments generally produce their effects by the vibrations of a column of air confined at one end, and either open or shut at the other. These vibrations are determined mainly by the length of the sounding column; yet inferior and subordinate ones are found to coexist with the fundamental one. The whole column spontaneously divides itself into portions equal to the half, the third, or the fourth of its longitudinal extent. In mixed wind-instruments, the vibrations or alterations of solid bodies are made to cooperate with the vibrations of a given portion of air. Thus, in the trumpet, and in horns of various kinds, the force of inflation, and perhaps the degree of tension of the lips, determines the number of parts into which the tube is divided, and the harmony which is produced. In the serpent the lips cooperate with a tube, of which the effective length may be varied by opening or shutting holes; and the instrument which has been called an organised trumpet, appears to act in a similar manner.
The trombone has a tube which slides in and out at pleasure, and changes the actual length of the whole instrument. The hautboy and the clarionet have mouth-pieces of different forms, made of reeds or canes; and the reed-pipes of an organ, of various constructions, are furnished with an elastic plate of metal, which vibrates in unison with the column of air which they contain.
The longitudinal vibrations of a column of air, contained within a tube open at both ends, are powerfully excited, and very loud and clear tones produced by the inflammation of a streamlet of hydrogen gas. This curious experiment was first made in Germany, and it is very easily performed. A phial, being partly filled with dilute sulphuric acid, a few bits of zinc are dropped into the liquid. As the decomposition of the water embodied with the acid now proceeds, the hydrogen gas, thus generated, flows regularly from the aperture. The gas being first ignited, and a glass tube placed over the exit-pipe, the burning speck at its point instantly shoots into an elongated flame, and creates a sharp and distinct musical sound. This effect is not owing to any vibrations of the tube itself; for it is in no way altered by tying a handkerchief tightly about the glass, or even by substituting a cylinder of paper. The tremor excited in the column of air is, therefore, the sole cause of the incessant tone, which only varies by a change in the place ofthe flame, or a partial obstruction applied at the end of the tube. The exciting force must necessarily act by starts, and not uniformly.
The column of air contained within the tube is in reality agitated by a series of incessant strokes, or sudden expansion; and it is probable, that an instrument possessing great power in a small compass, might be thus constructed.