1889.] Properties of Vulcanised India-rubber. 243 



The measures of n from each specimen are given below. Many 

 experiments were made, all agreeing very closely. 



2R = 28-4 in. I = 11*2 in. X = 1075. W = 100 grains. 



Soft grey. 

 r = 0-1560 in. 



Red. 

 r = 0-1607 in. 



Hard grey. 

 r = 0-1547 in. 



X. 



0. 



n. 



X. 



0. 



n. 



X. 



<p. 



n. 



2-25 

 2-3 



0-785 

 0-80 



65-68 

 65 51 



2- 3 



3- 16 



0- 915 



1- 268 



50 -76 

 50-33 



4- 20 



5- 05 



0-612 

 0-73 



161 -4 



162 -4 



(4.) Rigidity, Dynamical Measure. 



The small weights hung from A being removed, the periods of the 

 torsional oscillations of AB about DB were observed. 



Let T = the time of oscillation, 



w = weight of AB, 



g = acceleration of gravity in inches and seconds. 



Then for the other quantities involved, the notation being the same 

 as in (3), 



_ SwivRH 

 n ~ 3TV*gr ' 



For both the grey kinds of india-rubber the period varied consider- 

 ably with the arc of vibration, owing partly to the extinction of the 

 vibration being so rapid. The results were as follows : — 



Soft grey. 



Red. 



Hard grey. 



Arc. 



T. 



n. 



Arc. 



T. 



n. 



Arc. 



T. 



n. 



o 



60 

 30 

 10 

 5 



13 -2 

 12-7 

 12 -0 

 11-5 



80 -6 

 to 

 127-3 



60 

 30 

 10 

 5 



14-8 

 14-9 

 14-8 

 14-9 



56-85 



o 



60 

 30 

 10 

 5 



9-4 

 8-8 

 8-55 

 8-4 



156 

 to 

 202-6 



What the explanation is of the very large values for n given by this 

 method for the soft grey india-rubber, I have not been able to find 

 out. 



