HALLOWELL DAVIS 



67 



threshold as a function of frequency are shown in figure 7 (4). We need not 

 describe the methods by which these ampHtudes have been measured and cal- 

 culated, but we must note that their order of magnitude is of atomic and even 

 sub-atomic dimensions! And the corresponding calculations of the amount of 

 energy involved point to an energy level that is of the same order of magnitude 



Id' 



-10 



10 



10"' 



10 



10 



12 



13 



.-14 



\ \ \ 1 1 1 



Wavelengths of visible spectrum 



Amplitude of basilar membrane 

 (threshold of feeling) 



> 



Range of 

 uclear radii 



Range of X-ray^ 

 wavelengths 



_Amplitude of basilar membrane 

 (threshold of hearing) 



Cosmic ray^ 

 wavelengths^ 



10 



Frequency in cps 



Fig. 7. Amplitude of movement of the ear drum membrane al the threshold of human 

 hearing. Open circles are extrapolated from measurements of actual movement by Wilska; 

 solid line is derived from calculations based on measurements of threshold sound pressures. 

 From von Bekesy and Rosenblith (4), by permission. 



as that of the thermal energy that is responsible for Brownian movements. 

 Such minute amounts of energy delivered to one end of a hair cell can hardly 

 suffice to initiate nerve impulses at the other end without the interposition of a 

 trigger mechanism to amplify the available energy, and even this trigger itself 

 must be very delicately poised! 



The requirement of a 'biological amplitier' suggests that we should seek a pool 



