ANIMAL MECHANICS. 



19 



The tinnitus is altogether independent of muscular or vo- 

 luntary action of any kind, and is, I believe, a sign of the rate 

 at which nervous action takes place in the brain. 



The sound of the muscular susurrus, when fully heard, 

 is ridiculously like the sound of the cab wheels of London 

 heard in the silence of the night, when the absence of tho- 

 roughfare in the streets enables the cabmen to drive fats. I 

 have measured the intervals of the Guernsey granite pave- 

 ment, and found them to be about four inches, making there- 

 fore three impulses in a foot traversed by the cab wheels. If 

 the cabs be supposed to drive eight miles an hour, the number 

 of impulses per second will be 



C28o x q x 8 



< = 35- 2 - 



3600 JJ 



Considering that the standard DDD of the susurrus is thirty- 

 six vibrations per second, its resemblance to the sound of cab 

 wheels ceases to be a matter of surprise. 



In order to determine the sound of the susurrus precisely, 

 I procured a long wooden tube, 3 inches by 2 J inches inside, 

 like an organ pipe, fitted with a moveable piston, so that on 

 applying it to an acoustical bellows, on moving* the piston 

 in or out, I could produce any note I pleased in the neigh- 

 bourhood of CCC. This pipe is tuned, by means of the piston, 

 to the susurrus of any observer, and then played in conjunc- 



the resonance of the skull which contains the brain. The following observa- 

 tion throws light on this subject. On the 26th August, 1863, I received a vi- 

 olent blow from a racket ball in the back of the head, which partially stunned 

 me; and I was conscious at the instant of receiving the blow of a loud singing 

 sound in both ears, which I attributed to the vibration of the brain case, trans- 

 mitted to the cochleae aurium. This ringing sound seemed to me to have the 

 same pitch as the singing that occasionally occurs in my ears. 



* The piston is moved in the acoustical tube by means of an endless chain 

 movement, made for me by Mr. Spencer, of Aungier-street. 



c 2 



