of Solid Bodies by Internal Resistances. 167 



threads the deadening increases in general considerably with 

 increase in the duration of vibration. 



Only, for the longest caoutchouc thread examined (of 328 

 millims.) no increase occurred for small values of the duration of 

 vibration, but even a small decrease. 



All the other threads investigated (fine silk, glass, metal 

 threads) exhibited the same deportment, in reference to all pe- 

 riods of vibration examined, as did this longest caoutchouc thread 

 for small values of the duration of vibration; for in all was 

 there a decrease in the deadening with increase in the duration 

 of vibration. 



This complication of the phenomena might arise from the cir- 

 cumstance that e (the magnitude observed) is a compound one. 

 The deadening forces to which the vibrating system is subject 

 are partly to be sought outside it, in the resistance of the air, 

 and partly within it, in the thread itself. The results obtained 

 seemed to indicate that both parts of which the deadening con- 

 sists varied inversely as the duration of vibration. This supposi- 

 tion was confirmed by experiments being made in vacuo. The 

 apparatus was suitably changed for this purpose, so that the 

 pressure of the air could be reduced to 5 millims., and during 

 one experiment did not increase by more than 2 millims. From 

 this modification* it resulted that : — 



1. In the case of all threads, that part of the deadening (y) 

 arising from the internal resistance increases with the increase of 

 the duration of vibration. There was obtained, for instance : — 



Metal. 



T. V. 



8-7 0-000606 



3-7 0-000498 



Caoutchouc. 



4-3 0000843 



3-8 0000727 



Hence, with the same length of thread, the slower vibrations are 

 more powerfully deadened by the internal resistance than the 

 quicker ones. 



2. That part of the deadening (a) arising from the resistance 

 of the air decreases with increased duration of vibration r. There 

 was obtained, for instance : — 



8-7 0-000309 



3-7 0-000535 



* The method used of eliminating the resistance of the air is not strictly 

 correct according to O. E. Meyer (Pogg. Ann. vol. cxxv. p. 576 et seq.), 

 but is sufficient for the present object. 



