246 HERMANN VON HELMHOLTZ 



the external movable parts of the body, whereby the excited 

 state of certain fibres is preferentially transmitted to con- 

 sciousness/ 



These investigations speedily became the starting-point for the 

 most important discoveries of modern psycho-physics. With 

 them Helmholtz closed the series of his purely physiological 

 investigations, and turned in the first place to the mechanics of 

 physiology, and then almost exclusively to physics and mathe- 

 matics, in which he once more did epoch-making work. 



The results communicated by Helmholtz under the title of 

 'The Mechanics of the Auditory Ossicles' on July 26 and 

 August 9, 1867, at Heidelberg, and at greater length in the year 

 1869, in Pfliiger's Archiv, as * The Mechanics of the Auditory 

 Ossicles and of the Tympanum ' (which dealt with the very com- 

 plicated minute anatomy of the inner ear, and in which Helmholtz 

 discussed the mechanism of the oscillations of the tympanum 

 and small bones of the ear), were of supreme importance for the 

 mechanics of physiological acoustics. Riemann, * that unusually 

 penetrating intellect/ had indicated in a note published after his 

 death in the Zeitschrift f. rationelle Medicin, that the capital task 

 of aural mechanics was to explain how the apparatus of the 

 tympanic cavity was able to transmit such excessively fine 

 gradations of aerial waves to the fluid of the labyrinth. He 

 had constructed a theory to this end, based on the assumption 

 that the tympanic apparatus conveyed the alterations of air 

 pressure from moment to moment with exact fidelity, in a 

 constant ratio of magnification, to the fluid of the labyrinth. 

 Helmholtz, on the contrary (who had taken up this subject 

 directly he had concluded his Physiological Optics, without 

 knowing of Riemann's note), finds in his theoretical considera- 

 tions that it is only necessary for exact perception that each 

 tone of constant pitch should excite a sensation of the same 

 kind and intensity as often as it recurs. 



' Riemann's acoustic problem/ writes Helmholtz to Schering 

 'occupied me also for some time; the empirical solution as 

 effected for the human ear is, as a matter of fact, different from 

 what he supposed/ Starting from the assumption that had been 

 merely suggested by Ed. Weber, that the auditory ossicles and 

 the petrosal bone must be regarded as fixed incompres- 

 sible bodies, and the endolymph as an incompressible fluid, in 



