158 HERMANN VON HELMHOLTZ 



agrees with the rapid alternations of electrical distribution in 

 nerve, and it looks as if the lag in the above effects must occur 

 in the fibres of the muscle and the portions of the retina that 

 are sensitive to light.' 



By the end of the year his Theory of Vowel Tones, with 

 which he had been occupied for months, was so far advanced 

 that he was able on November 4, 1857, to tell Bonders that 

 they were distinguished by the higher partial tones which 

 accompany the prime tone. By singing into a piano, it is easy 

 in pronouncing a, o, e to set the strings corresponding to the 

 upper partial tones into vibration ; it is only necessary to sing 

 the tone exactly, and keep it on; the experiment succeeds 

 best with practised singers, 'with my wife better than myself.' 

 If the fundamental tone is called the first tone, and the higher 

 partials, with two, three, four, &c. times as many vibrations, are 

 termed the second, third, fourth, &c., then when a is sung the 

 third and fifth tones are heard plainly with the first, while 

 the second, fourth, and seventh are weaker ; with o the third 

 is rather weaker than with a, while the second and fifth are 

 very feeble ; with u the prime is almost the only tone audible, 

 the third is weak ; with e the second is very marked, the upper 

 tones are scarcely audible; and with i the clear character of 

 the vowel seems to depend on second and third tones pre- 

 ponderating over the weak ground-tone, while the fifth is heard 

 feebly. 



There were still, however, great difficulties to overcome 

 before the Vowel Theory could be completely established, and 

 Helmholtz was occupied with these till the beginning of 1859. 

 ' In the next place I must attack the problems relating to the 

 origin of timbre (Klangfarbe), since these will solve the funda- 

 mental problem of physiological acoustics discussed by Ohm 

 and Seebeck : what kind of vibration corresponds with a single 

 audible tone ? I believe Ohm to be right in his view that the 

 ear analyses and hears the motions of the air in exact corre- 

 spondence with Fourier's theorem/ he writes to Bonders in 

 the letter above quoted. 



It was many years since Helmholtz had discussed his philo- 

 sophical position with his father. On Becember 17, he 

 writes : 



'All goes well here, we are all flourishing. My official 



