SECT. XVII. VIBRATION. 143 



half as long as the tube, the second harmonic by waves a third 

 as long, and so on. The harmonic segments in an open and 

 shut pipe are the same in number, but differently placed. In a 

 shut pipe the two ends are nodes, but in an open pipe there is 

 half a segment at each extremity, because the air at these points 

 is neither rarefied nor condensed, being in contact with that 

 which is external. If one of the ends of the open pipe be closed, 

 its fundamental note will be an octave lower : the air will now 

 divide itself into three, five, seven, c., segments ; and the wave 

 producing its fundamental note will be twice as long as the pipe, 

 so that it will be doubled back (N. 182). All these notes may 

 be produced separately by varying the intensity of the blast. 

 Blowing steadily and gently, the fundamental note will sound ; 

 when the force of the blast is increased the note will all at once 

 start up an octave ; when the intensity of the wind is augmented 

 the twelfth will be heard ; and, by continuing to increase the 

 force of the blast, the other harmonics may be obtained, but no 

 force of wind will produce a note intermediate between these. 

 The harmonics of a flute may be obtained in this manner, from 

 the lowest C or D upwards, without altering the fingering, 

 merely by increasing the intensity of the blast and altering the 

 form of the lips. Pipes of the same dimensions, whether of lead, 

 glass, or wood, give the same tone as to pitch under the same 

 circumstances, which shows that the air alone produces the 

 sound. 



Metal springs fastened at one end, when forcibly bent, endea- 

 vour to return to rest by a series of vibrations, which give very 

 pleasing tones, as in musical boxes. Various musical instruments 

 have been constructed, consisting of metallic springs thrown 

 into vibration by a current of air. Among the most perfect of 

 these are Mr. Wheatstone's Symphonion, Concertina, and ^Eolian 

 Organ, instruments of different effects and capabilities, but all 

 possessing considerable execution and expression. 



The Syren is an ingenious instrument, devised by M. Cagniard 

 de la Tour, for ascertaining the number of pulsations in a second, 

 corresponding to each pitch : the notes are produced by jets of 

 air passing through small apertures, arranged at regular distances 

 in a circle on the side of a box, before which a disc revolves 

 pierced with the same number of holes. During a revolution of 

 the disc the currents are alternately intercepted and allowed to 



