160' . VIBRATION OF SPRINGS AND RODS. [SECT. xvn. 



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 pro- 

 duces the sound. 



Metal springs fastened at one end, when forcibly bent, 

 endeavour to return to rest by a series of vibrations, which 

 give very pleasing tones, as in musical boxes. Various 

 musical instruments have recently been constructed, con- 

 sisting of metallic springs thrown into vibration by a cur- 

 rent 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 pos- 

 sessing considerable execution and expression. 



The Syren is an ingenious instrument, devised by M. 

 Cagniard de la Tour, for ascertaining the number of pulsa- 

 tions 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 pass as many times 

 as there are apertures in it, and a sound is produced whose 

 pitch depends on the velocity of rotation. 



A glass or metallic rod, when struck at one end, or 

 rubbed in the direction of its length with a wet finger, 

 vibrates longitudinally like a column of air, by the alter- 

 nate condensation and expansion of its constituent par- 

 ticles, producing a clear and beautiful musical note of 

 a high pitch, on account of the rapidity with which 

 these substances transmit sound. Rods, surfaces, and, in 

 general, all undulating bodies, resolve themselves into 



