1889.] 



Properties of Vulcanised India-rubber. 



247 



mi Vic'p 



Then k = -7 7^77 — ^tt- 



As a test of the accuracy of the method, the volume elasticity of 

 water was measured. The value found for k was 296,000 lbs. per 

 square inch, a result which is not far from the truth. 



The values for india-rubber were 



Km 



Soft grey 198,000 



Red 115,000 



Hard grey 940,000 



These values are the means of all the experiments after the first. 

 The first application of pressure, however, always produced a much 

 more considerable compression, and if the volume of elasticity had 

 been deduced from the first experiment only, its value would have 

 been about half that given above in the case of the soft grey and red ; 

 and for the hard grey, about one-eighth. 



(7.) Viscosity. 



The rate at which the vibration iu Experiment (4) died away was 

 used to determine the coefficient of viscosity. 



Diagram IY gives the " curves of extinction " for the three kinds of 

 india-rubber. The ordinate of the curve is at each point, the ampli- 



Diagram IY. 



