138 VIBRATION OF SPRINGS AND RODS. SECT. XVII. 



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, endeavor to return to rest by a series of vibrations, 

 which give very pleasing tones, as in musical boxes. 

 Various musical instruments have recently been con- 

 structed, consisting of metallic springs thrown into vibra- 

 tion by a current of air. Among the most perfect of these 

 are Mr. Wheatstone's Symphonion, Concertina, and JE>o- 

 lian 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 Devolves 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 ir 

 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 genera], all, undulating bodies, resolve themselves into 

 nodes. But in surfaces, the parts which remain at rest 

 during their vibrations are lines, which are curved or 

 plane according to the substance, its form, and the mode 

 of vibration. If a little fine dry sand be strewed over 

 the surface of a plate of glass or metal, and if undula- 

 tions be excited by drawing the bow of a violin across 

 its edge, it will emit a musical sound, and the sand 

 will immediately arrange itself in the nodal lines, where 

 alone it will accumulate and remain at rest, because the 



