HELMHOLTZ IN BONN 



of the drumhead in a satisfactory manner. Had the 

 drumhead been a uniformly flat-stretched membrane, 

 the amplitude of its movements, in response to the 

 varying pressures of sound waves, would be greatest 

 in the centre, while it would diminish as the periphery 

 of the membrane was approached. Helmholtz showed 

 that it is not flat, but composed of numerous fibres so 

 arranged as to present the convexity of a curve out- 

 wards, that is, meeting the sound waves falling upon 

 them, while the membrane, as a whole, bulges in- 

 wards. In this way a very small change in the 

 pressure of the air causes a considerable increase in 

 the tension of the fibres, and as the force exerted 

 upon the handle of the malleus (the bone attached 

 to the membrane) increases, the amplitude of the 

 movement of that bone diminishes. Thus the special 

 form of the drumhead secures a maximum of efficiency 

 for tones of the feeblest intensity. 



He then proceeds to examine the mechanism of the 

 chain of bones, showing that they constitute a lever 

 in which the force is applied at the handle of the 

 malleus where it is attached to the membrane, the 

 fulcrum where the short process of the incus abuts 

 against the wall of the tympanum, and the work is 

 done at the base of the stapes, where it pushes into 

 the oval window, on the other side of which we 

 have the labyrinth. The lever is such as to diminish 

 the amplitude of the movements at the base of the 

 stapes, while the work is done over a smaller area 

 '35 



