35G Prof. A. ^1. Mayer's Experiments on the supposed 



The Table of experiments wliicli I have given is characteristic 

 of all of the many scries which I have made. In the first column 

 (A) I have given the notes of the forks in the French notation, 

 whicii Konit; stamps upon his forks. In the second (B) are the 

 am})litudes of the vibrations of the end of the tibril in divisions 

 of the micrometer-scale; and in column C are the values of 

 these divisions in fractions of a millimefrc. 



The superior effect of the vibrations of the Ut, fork on the 

 fibril is marked ; but thinking that the differences in the ob- 

 served amplitudes of the vibrations might be owing to differ- 

 ences in tlie intensities of the various sounds, I repeated the 

 experiment, but vibrated the forks which gave the greater ampli- 

 tudes of covibration with the lowest intensities; and although I 

 observed an approach toward equality of amplitude, yet the 

 fibril gave the maximum swings when Ut, was sounded ; and I 

 was persuaded that this special fibril was tuned to unison with 

 Ut, or to some other note within a semitone of it. The differ- 

 ences of amplitude given by Ut, and S0I3 and Mi, are con- 

 siderable ; and the Table also brings out the interesting ob- 

 servation that the lower (Utg) and the higher (Ut^) harmonics 

 of Ut, cause greater amplitudes of vibration than any interme- 

 diate notes. As long as a universal method for the determina- 

 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 



• I have recently made some exjieriments in this direction, which show 

 the possibihtv of eventually being able to exi)iess the intensity of an ai'rial 

 vibration directlv infraction of Joule's dynamical unit, by measuring the 

 heat developed in a slip of sheet rubber stretched between the j)rongs of a 

 fork and enclosed in a comjjound thermo-batterv. The relative intensities 

 of the aerial vibration produced by the fork w lien engaged in heating the 

 rubber and when the ruljber is removed, can be measured l)y tiie method I dc- 

 S(rd)ed in the Philosophical Magtizine, lS7.'i, vol. xlv. p. IH. Of course, if we 

 candeteruune tbeauKimit of heat produced per second by a kno«n fraction of 



