HERMANN VON HELMHOLTZ 



be well adapted for sympathetic resonance, but, as 

 they were of small mass, they could not long continue 

 their motion. Again, according to him, the am- 

 pullae at the ends of the semi-circular canals, in which 

 there are also nerve-endings similar to those in the 

 crista, being wide cavities with narrow exits, are 

 suitable for producing a central current, which partly 

 passes into eddies, and these would deflect the bristles, 

 causing an oscillation. A movement of the whole 

 mass of the bristle, floating in the fluid, would not 

 serve the same purpose, but discontinuous streams of 

 different strengths and in different directions would 

 do so effectively. Thus Helmholtz contributed to 

 our knowledge of what may take place in the saccule 

 and utricle and ampullae. Researches made since his 

 time have suggested that these parts may not have to 

 do, strictly speaking, with hearing, but with the re- 

 ception of those greater variations of pressure on 

 which the sense of equilibrium depends. They may 

 have to do with the appreciation of mass movement, 

 and only indirectly with those more delicate variations 

 of pressure on which true hearing depends. 



Hitherto we have considered only the reception of 

 simple harmonic (sometimes termed simple pendular) 

 vibrations which are known to be physically re- 

 lated to pure tones. The sensation of a pure tone, 

 such as can be excited by carefully bowing a 

 tuning fork, mounted on a resonance box, or by 

 an open organ pipe caused to sound gently by a 

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