1889.] Properties of Vulcanised India-rubber. 235 



DlAGEAM I. 



Diagrams I and II illustrate these properties, which are probably 

 possessed to a very minute degree by many substances usually con- 

 sidered perfectly elastic. 



From these diagrams it will be seen that the two elastic constants, 

 viz., Young's modulus and the rigidity, are not completely defined 

 nnless the time is given for which the force calling them into play 

 acts. 



Another property of india-rubber, especially conspicuous in the soft 

 grey kind, is that when stretched to a certain point the resistance to 



