1889.J 



Properties of Vulcanised India-rubber. 



241 



It will be noticed that the values of q thus obtained are much 

 greater for the soft grey and red varieties than those obtained 

 statically, and the chief part of this difference is due to their not 

 having time to take the subpermanent set which they would acquire if 

 the period was very long, but in part also it must be due to a thermo- 

 dynamic cause. 



(3.) Simple Rigidity. Statical Measure. 

 The arrangement shown in fig. 4 was used for both the statical 

 and dynamical measures of the rigidity. 



Fig. 4. 

 D 



The india-rubber was held at each end by clamps of sheet brass C, C 

 shown in section in fig. 5. 



Through the lower part of C the rod P passes, which fixes its 

 position rigidly. The upper clamp C is attached to the bar AB, this 

 bar being suspended in a horizontal plane by two silk threads from 

 the point D. A small plumb-bob is also hung from D to facilitate the 

 centering of the upper clamp and the divided circle F. When the 



s 2 



