198 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



It is seen from the above experiment that the pressures re- 

 quired to sound wind instruments are small, when it is known 

 that Dr. Stone found that the musicians could support with 

 their lips a pressure of six feet of water. Philosophical Mag- 

 azine, XLVIII., 114. 



ON THE DURATIONS OF SONOROUS SENSATIONS. 



Professor Mayer, in paper No. 6 of his series of " Research- 

 es in Acoustics," gives his discovery of the law connect- 

 ing the pitch of a sound with the time during which its sen- 

 sation remains in the ear after the vibrations causing this 

 sound have ceased outside the ear. These after-sensations 

 are called residual sensations. He finds that the residual 

 sensation of the treble C, of 256 vibrations per second, lasts 

 -5V of a second; the lowest audible sound, produced by 40 

 vibrations per second, lasts in the ear -^ of a second, while 

 the highest audible sound, of 40,000 vibrations per second, 

 endures only -^-J^ of a second. 



The knowledge of the above law (which has for its expres- 

 sion the following formula, D = f? -f24Yo001, in which 



VN + 23 / 



D is the duration of the residual sensation, and N is the num- 

 ber of vibrations per second of the sound corresponding to 

 D) has shed much light on various obscure points in the 

 physiology of audition. Among other results, it has ex- 

 plained why we do not have a continuous sonorous sensation 

 from vibrations fewer than 40 per second; it has confirmed 

 Helmholtz's views of the hiarh differentiation of the func- 



CD 



tions of the sensory apparatus of the ear ; it has rendered 

 quantitative much of Helmholtz's work on the physiological 

 theory of music ; and has led to the curious discovery that 

 a composite sound can be analyzed into its elementary sim- 

 ple sounds, or harmonics, by means of a perforated rotating 

 disk. Thus, if a large disk, with sectors cut out of it, is rap- 

 idly revolved between the ear and a reed-pipe (which always 

 gives a highly composite sound), we shall have the compo- 

 site sound reaching the ear in a series of impacts, which suc- 

 ceed each other so rapidly that even those of the highest 

 harmonic of the reed blend into a continuous sensation; but 

 on gradually lowering the velocity of rotation, the impacts 

 of this highest harmonic can no longer blend, and we per- 



