THE SIX GATEWAYS OF KNOWLEDGE. 269 



tympanum unless means be adopted for obviating 

 the difference in the pressures ; but the simple 

 means I have indicated are, I believe, with all 

 ordinary healthy persons, perfectly successful. 



I am afraid we are no nearer, however, to under- 

 standing what it is we perceive when we hear. 

 To be short then it is simply this : it is exceedingly 

 sudden changes of pressure acting on the tym- 

 panum of the ear, through such a short time and 

 with such moderate force as not to hurt it ; but 

 to give rise to a very distinct sensation, which is 

 communicated through a train of bones to the 

 auditory nerve. I must merely pass over this ; the 

 details are full of interest, but they would occupy 

 us far more than an hour if I entered upon them 

 at all. As soon as we get to the nerves and the 

 bones, we have gone beyond the subject I proposed 

 to speak upon. My subject belongs to physical 

 science ; what is called in Scotland, Natural 

 Philosophy. Physical science refers to dead matter, 

 and I have gone beyond its range whenever 

 1 speak of a living body ; but we must speak of 

 a living body in dealing with the senses as the 



