THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



MARCH 1870. 



XXI. On the Deadening of the Sounds of Solid Bodies by Internal 

 Resistances. By Dr. E. Warburg*. 



IT is a well-known fact that the sound-vibrations of solids 

 gradually become extinguished when they are not sustained 

 by external force. The causes of this extinction are partly ex- 

 ternal — resistance of the surrounding medium, friction against 

 the points at which the bodies are fastened, and communication 

 of motion to them — and partly internal, depending on the nature 

 of the solid itself. The existence of such internal causes was 

 originally demonstrated by Wilhelm Weber in the torsion vibra- 

 tions of a silk thread ; for he found that they became extinguished 

 in a short time even in vacuo. There can here be no appreciable 

 communication of motion to the point of suspension, so that the 

 forces which in this case produce the extinction must be sought 

 in the structure of the vibrating thread. 



The forces which, acting in the interior of solids, bring about 

 the extinction of their vibrations, will be denoted in the sequel 

 as the internal resistance of solids. 



In reference to the internal resistance of solids, Helmholtz 

 remarkst: — "More perfect elasticity seems peculiarly to favour 

 the continuance of the higher tones ; for more rapid vibrations 

 are in general more quickly deadened by imperfect elasticity and 

 friction than slower ones/' 



The author is not aware of any experimental proof that higher 



* Translated from the Berliner Monatsbericht for July 1869. 

 t Lehre von den Tonempjindungen, p. 122. 



Phil Mag. S. 4. Vol. 39. No. 260. March 1870. M 



