190 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



The author considers his result as only approximative, yet 

 it is interesting as the first determination of this kind ever 

 made, and valuable as conveying an idea of the amount of 

 mechanical energy necessary to produce definite sonorous 

 vibrations in the air. We can not do better than quote from 

 Professor Mayer's paper : 



"In the following manner I have recently made experi- 

 ments in the direction of determining the equivalent of a 

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

 of 772 foot-pounds. I stretched between the prongs of a 

 Ut 3 tuning-fork a piece of sheet caoutchouc, T ~ of an inch 

 in thickness, and about half an inch broad. The eiiect 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 former. By a method 

 described by me in the American Journal of Science, Feb- 

 ruary, 1871, 1 measured the relative intensities of the aerial 

 vibrations on these two conditions of their production. The 

 sheet of caoutchouc was inclosed in a compound thermo-bat- 

 tery, and the fork vibrated during a known interval; the 

 rubber was heated by the vibrations, which would have ap- 

 peared as sonorous vibrations if the rubber had been removed 

 from the fork. The amount of heat given to the caoutchouc 

 was accurately determined by observing the deflections of'a 

 Thomson's reflecting-galvanometer connected with the ther- 

 mo-battery ; and by knowing the time during which the fork 

 vibrated the amount of heat given to the caoutchouc during 

 this time, and the equivalent of the heated rubber in heated 

 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 pro- 

 duced during ten seconds by a Ut 3 fork placed in front of 

 its resonator equaled about 100 * 000 of a Joule's unit ; that 

 is, these aerial vibrations can be expressed in the work done 

 in lifting 54 grains one foot high. This quantity of heat is 

 equal to the heating of one pound of water 100 % 00 of a de- 



