ANIMAL MECHANICS. 



21 



Hence, 



40 , 



showing that the pitch of his muscular susurius conesponded 

 to 30 vibrations per second. 



The preceding investigation of the precise sound of the 

 muscular susurrus was published by me in 1 863, having formed 

 part of a thesis for a medical degree in the University of 

 Dublin in 1862; and shortly after its publication, Dr. Col- 

 longues, of Paris, forwarded to me a copy of a work published 

 by him in 1862 (" Traite de Dynamoscopie,"8vo, Paris, 1862), 

 in which he had solved the same problem, and found an iden- 

 tical result from his acoustical experiments. Dr. Collongues 

 attempted to determine the pitch of the susurrus, with com- 

 plete success, by means of a tuning fork, with sliding weights, 

 which was put into unison with the susurrus, and then com- 

 pared carefully with a standard tuning fork, whose time of 

 vibration was determined graphically by the aid of a black- 

 ened revolving cylinder, which was marked with a zigzag 

 line by a pin attached to one arm of the vibrating fork. The 

 note fixed on by Dr. Collongues was Re_i, or 72 vibrations 

 per second, reckoned in the French fashion by half vibrations, 

 and corresponding to 36 vibrations per second of English 

 acousticians. I readily accord to Dr. Collongues the pri- 

 ority of publication of the exact determination of the pitch of 

 Wollaston's susurrus, and believe it to be a matter of some 

 interest to science that two independent observers, by different 

 methods, one in Paris, and the other in Dublin, succeeded in 

 arriving at a precise and almost identical value for this im- 

 portant physiological constant. 



Dr. Collongues believes that the susurrus is caused by the 

 nerves, and not by the muscles, and the greater part of his 

 valuable book is taken up with an account of the variations of 

 the susurrus inhealth and in disease. With this part of his inves- 



