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



tion of the relative intensities of sounds of different pitch re- 

 mains undiscovered, so long will the science of acoustics remain 

 in its present vague qualitative condition*. Now, not having 

 the means of equalizing the intensities of the vibrations issuing 

 from the various resonant boxes, 1 adopted the plan of sounding 

 with a bow each fork with the greatest intensity I could obtain. 

 I think that it is to be regretted that Konig did not adhere 

 to the form of fork with inclined prongs as formerly made by 

 Marloye; for with such forks one can always reproduce the 

 same initial intensity of vibration by separating the prongs by 

 means of the same cylindrical rod, which is drawn between 

 them. Experiments similar to those already given revealed a 

 fibril tuned to such perfect unison with Ut 3 that it vibrated 

 through 18 divisions of the micrometer, or *15 millim., while 

 its amplitude of vibration was only 3 divisions when Ut 4 was 

 sounded. Other fibrils responded to other notes; so that I infer 

 from my experiments on about a dozen mosquitos that their 

 fibrils are tuned to sounds extending through the middle and 

 next higher octave of the piano. 



To subject to a severe test the supposition I now entertained, 

 that the fibrils were tuned to various periods of vibration, I mea- 

 sured with great care the lengths and diameters of two fibrils, 

 one of which vibrated strongly to Ut 3 , the other as powerfully 

 to Ut 4 ; and from these measures I constructed in homogeneous 

 pine-wood two gigantic models of the fibrils, the one corre- 

 sponding to the Ut 3 fibril being about 1 metre long. After a 

 little practice I succeeded in coucting readily the number of 



* I have recently made some experiments in this direction which show 

 the possibility of eventually being able to express the intensity of an aerial 

 vibration directly in fraction of Joule's dynamical unit, by measuring the 

 heat developed in a slip of sheet rubber stretched between the prongs of a 

 fork and enclosed in a compound thermo-battery. The relative intensities 

 of the aerial vibration produced by the fork when engaged in heating the 

 rubber and when the rubber is removed, can be measured by the method I de- 

 scribed in the Philosophical Magazine, 1873, vol. xlv. p. 18. Of course, if we 

 can determine the amount of heat produced per second by a known fraction of 

 the intensity, we have the amount produced by the vibration with its entire 

 intensity. Then means can be devised by which the aerial vibration pro- 

 duced by this fork can always be reproduced with the same intensity. 

 This intensity, expressed in fraction of Joule's unit, is stamped upon the 

 apparatus, which ever afterward serves as a true measure for obtaining the 

 intensities of the vibrations of all simple sounds having the same pitch as 

 itself. The same operation can be performed on other forks of different 

 pitch ; and so a series of intensities of different periods of vibration is ob- 

 tained expressed in a corresponding series of fractions of Joule's unit. 

 Recent experiments have given -■ o o 1 Q - o of a Joule's unit as the approxi- 

 mate dynamic equivalent of ten seconds of aerial vibrations produced by 

 an Ut 3 "fork set in motion by intermittent electromagnetic action and placed 

 before a resonator. 



