PAPERS PRESENTED AT GENERAL SESSIONS 41 



ears. Expressed in terms of physical intensity, the am- 

 plification reqnired to produce normal sensitivity for this 

 observer is of the order of 100,000 fold. The best of the 

 ear trumpets produced a magnification of some twenty 

 fold, while the telephone at the frecpiency for which it 

 was most efficient magnified the intensity some two hun- 

 dred fold. 



Study of the ear, regarded simply as a piece of physi- 

 cal apparatus, has been a field of investigation sadly 

 neglected by physicists. "What is known of the perform- 

 ance of the ear in a quantitative way is lamentably small. 

 Otologists readily admit that the physical methods they 

 are forced to employ for want of better are deplorably 

 inadequate, as compared with similar methods employed 

 in the diagnosis of defects of vision. A program of inves- 

 tigation in this field has been begim. The first problem 

 attacked has been that of the determination in absolute 

 units of the mintmun sound intensity that will produce 

 the sensation of sound. The results of previous investi- 

 gations on this question have shown enormous differ- 

 ences. Thus Wien, working in Germany, obtained re- 

 sults indicating a sensitivity of normal ears for tones in 

 the middle and upper registers 10,000 times as great as 

 that determined by Lord Rayleigh. In our Laboratory, 

 ^Ir. F. W. Kranz has spent almost two years upon this 

 prol)lem. Using a number of methods, results have been 

 obtained, discordant at first, but now showing satisfac- 

 tory agreement, as sources of error have been eliminated 

 one after another. The energies to be measured are ex- 

 tremely small, and the experimental^ difficulties are great. 

 Perhaps the most striking of the results is the wide va- 

 riation of apparently normal hearing. Of the tAventy 

 normal ears examined, the least sensitive required for 

 the perception of the tone 512 vibrations, 100 times that 

 required by the most sensitive. At a pitch two octaves 

 above this, the maximum variation of sensitivity was by 

 a factor of 1,000. In general, the range of tones for 

 which the ear is most sensitive is the third octave above 

 middle C, where the sensitivity is about 10,000 times as 

 great as for the octave below this tone. In the region of 

 maximum sensitivity, Mr. Kranz' measurements indicate 



