FLUE-PIPES AND REEDS. 113
moreover is not quite flattened, but slightly curved away from the reed, so as to leave a thin gap between the end of the reed and the mouth piece. The Clarinet has thus only a single reed, and that a beating one.
The tube is pierced with eighteen holes, half of which are closed by the fingers, and half by keys. The lowest note is produced by closing all the apertures and blowing gently. By opening successively the eighteen apertures, eighteen other notes may be obtained at intervals of a semitone ; and thus the lower scale, of one-and-a-half octaves, is obtained. By increase of wind pressure, or by opening an aperture at the back of the tube, the pitch of the tube is raised a twelfth; in fact the instrument acts like a stopped tube, increased wind pressure bringing out, not the second, but the third of the ordinary harmonic series.
The quality of tone on the Clarinet is very characteristic, and is due to the fact that only the odd partials, 1, 3, 5, 7, &c, are present in its tones; just as in the case of stopped organ pipes. In fact the Clarinet must be considered as such a pipe, stopped at the end where the reed is placed; for it is here that the greatest alternations of pressure occur; that is, as we have seen above, this point must be a node.
The Oboe and Bassoon have conical tubes expanding into bells. The reed in each is double and formed of two thin broad spatula-shaped plates of cane in close approximation to one another. Variations in pitch are obtained as in the flute, by varying the e ffective length of the tube, by means of apertures closed by the fingers or keys. Like the flute also, the first harmonic is the octave, so that increase of wind pressure raises the pitch by that interval. The partials present in the tones of these instruments, are those of the complete series, 1, 2, 3, 4, 5, &c.
In instruments with cupped mouth pieces, the lips of the player, which form the reed, are capable of vibrating at very different rates, according to their tension, form, &c. A very simple type of this class of instrument may be obtained, by placing a common glass funnel into |one end of a piece of glass tubing, a few feet long, and half an inch or so in diameter. The tones, which can be obtained from such a tube, by varying the tension and form of the lips and the force of the wind, are those of the complete partial series; the lowest ones are, however, very difficult to obtain. Thus no note can be produced on such an instrument, but such as bolong to the series of partials, or harmonic scale, as it is sometimes termed.