Vibrations on Gaseous and Liquid Jets. 381 



friction, which, when the force of transfer is sufficiently great, 

 throws the issuing stream into the state of vibration that pro- 

 duces flaring. It is because the flaring is thus caused that an 

 almost infinitely small amount of energy, applied in the form 

 of vibrations of the proper period, can produce an effect equiva- 

 lent to a considerable increase of pressure. Augmentation of 

 pressure is, in fact, a comparatively clumsy means of causing a 

 flame to flare*. 



All sounds are not equally effective on the^flame ; waves of 

 special periods are required to produce the maximum effect. The 

 effectual periods are those which synchronize most nearly with 

 the waves produced by the friction of the gas itself against the 

 sides of its orifice. With some of the flames which you have 

 already seen, a low deep whistle is more effective than a shrill 

 one. With the flame now before you, the exciting tremors must 

 be very rapid, and the sound consequently shrill. I have here 

 a tuning-fork which vibrates 256 times in a second, emitting a 

 clear and forcible note. It has no effect upon this flame. Here 

 also are three other forks, vibrating respectively 320, 384, and 

 512 times in a second. Not one of them produces the slightest 

 impression upon the flame. But, besides their fundamental 

 tones, these forks, as you know, can be caused to yield a series 

 of overtones of very high pitch. I sound this series : the vibra- 

 tions are now 1600, 2000, 2400, and 3200 per second respect- 

 ively. The flame jumps in response to each of these sounds, 

 the response to the highest sound of the series being the most 

 prompt and energetic of all. 



To the tap of a hammer upon a board the flame also responds ; 

 but to the tap of the same hammer upon an anvil the response 

 is much more brisk and animated. The reason is, that the clang 

 of the anvil is rich in the higher tones to which the flame is most 

 sensitive. 



The powerful tone obtained when our inverted bell is reinforced 

 by its resonant tube has no power over this flame. The bell is now 

 sounding, but the flame is unmoved. But when I bring a half- 

 penny into contact with the vibrating surface, the consequent 

 rattle contains the high notes to which the flame is sensitive. 

 It instantly shortens, flutters, and roars when the coin touches 

 the bell. I hold in my hand a smaller bell, the hammer of 



* As already remarked, a candle-flame is caused to flutter by its rapid 

 motion through the air ; and the vertical motion of the flame in the expe- 

 riments just described may help to produce the flaring. The principal 

 cause, however, I believe to be that above assigned. The gas within the 

 burner, and the air outside it, form a continuous medium, through which 

 the effective vibrations are transmitted both to the flame and the orifice 

 that feeds it. 



