Prof. A.M. Mayer's Researches in Acoustics. 431 



flame equals the intensity of the vibrations which impinged on 

 the flame minus the intensity of those which were reflected from 

 the flame, then there is no absorption of these vibrations by 

 the flame ; but if this equality does not exist, then there is 

 absorption in the flame; and this means that the flame is heated 

 by the sonorous vibrations — which enter the flame as sonorous 

 vibrations, but issue from the flame as heat vibrations. It thus, 

 at first, appears that the absorption of the sonorous vibrations 

 might be detected by their production of an increase in the 

 temperature of the flame, just as sonorous vibrations are absorbed 

 by caoutchouc and reappear as heat in this substance. 



In the following manner I have recently made experiments 

 in the direction of determining the equivalent of a given 

 sonorous aerial vibration in fraction of a Joule's unit of 772 

 foot-pounds. I stretched between the prongs of an Ut 3 tuning- 

 fork a piece of sheet caoutchouc, Thr inch in thickness, and 

 about ^ inch broad. The effect of this rubber on the vibrating 

 fork is rapidly to extinguish its vibrations, while the rubber 

 itself is heated ; and if a fork be vibrated continuously by one 

 and the same force when the rubber is stretched on it^ and then 

 when it is taken off, the aerial vibrations produced by the fork 

 are far more intense in the latter circumstances than in the for- 

 mer. By a method described by me in Feb. 1873, I measured 

 the relative intensities of the aerial vibrations in these two con- 

 ditions of vibration. The sheet of caoutchouc was enclosed in a 

 compound thermo-battery, and the fork vibrated during a known 

 interval ; the rubber was heated by the vibrations which would 

 have appeared as sonorous vibrations if the rubber had been re- 

 moved from the fork. The amount of heat given to the caout- 

 chouc was accurately determined by the deflections of a Thomson 

 reflecting-galvanometer connected with the thermo-battery ; and 

 by knowiDg the interval during which the fork vibrated, the 

 amount of heat given to the caoutchouc during this interval, and 

 the equivalent of the heated rubber in water, I calculated the 

 intensity of the sonorous vibrations in terms of a thermal unit, 

 from which I at once obtained the value of the sonorous aerial 

 vibrations when the fork was not heating the rubber- — in other 

 words, when it vibrated freely. I thus found that the sonorous 

 aerial vibrations produced during ten seconds by an Ut 3 fork 

 placed in front of its resonator, equalled about tfottw °f a 

 Joule's unit ; that is, they can be expressed by the work done in 

 lifting 54 grains one foot high. This quantity of heat, which 

 is equal to the heating of one pound of water TW&VTi o" °f a degree 

 Fahr., expressed the amount by which the gas-flame would be 

 heated if it absorbed all of the sonorous vibrations issuing from 

 the Ut 3 resonator. But this is such a small fraction of the 



