347 



the last meeting, which, in a very simple way, illustrate 



the origin t 



vibrations. 



the origin and some of the conditions of their musical 



(1.) When a jet of buniing coal-gas is introduced into the 

 resonant tube in a position in which it does not sing spontane- 

 ously, we may cause it to commence its musical performance by 

 simply vibrating the jet pipe rapidly from side to side. In this 

 experiment the pipe should be covered with soft buckskin for two 

 or three inches near its upper end, to prevent the sharp jarring 

 sound caused by its striking the glass. This movement of the 

 jet is so efficient in bringing on the sonorous state, that it will 

 compel the flame to sing, even in a tube in which it would not do 

 so spontaneously in any position in which we could place it. In- 

 deed, it will often excite the musical vibrations in cases where, 

 from the unsuitable proportions between the tube and flame, the 

 external sounds used in SchafFgotsch's and Tyndal's expei'iment 

 entirely fail to bring on the sonorous state. 



Although the singing is induced more promptly when we 

 allow the jet pipe in its vibrations to strike the sides of the tube, 

 this action is not at all necessary ; for we obtain the same result 

 when the pipe is merely shaken to and fro within such limits as 

 to prevent its touching the glass. The effect here described can 

 hardly fail, when first observed, to excite surprise, especially if 

 from previous trials we have found that the flame refuses either 

 to sing spontaneously or under the action of external sound. 



So far as the impulse of the jet pipe against the sides of the 

 tube is influential in exciting the sound, we must ascribe its action 

 to the feeble musical resonance produced by it wdthin the tube, 

 which, although composed of several sounds, may always be ob- 

 served to include the fundamental note of the tube. This action 

 is therefore like that of a unison note sounded by the voice or an 

 external instrument, or that of any other mechanical agency giving 

 rise to a vibration of the included column of air. But the other 

 and far more remarkable effect, the excitement of the musical 

 condition in the flame by simply moving it to and fro without 

 striking the tube, cannot be thus explained, since the gentle im- 

 pulse given to the air by the vibrating pipe produces no audible 

 effect and would seem quite inadequate to excite in the column 



