Caoutchouc or Indian Rubber. 293 



takes place in the figure of the thong. Now 

 if the existence of caloric be admitted, it will 

 follow from the preceding arguments, that the 

 phenomenon under consideration is occasioned 

 by the alternate absorption and emission of the 

 calorific fluid, in the same manner that ropes, 

 the blades of Fuci, as well as many more 

 bodies, are obliged to contract and extend them- 

 selves, by the alternate absorption and emission 

 of water. — You will perceive by the tenour of 

 the foregoing observations, that my theory of 

 this case of elasticity is perfectly mechanical ; 

 in fact, the explanation of it depends upon the 

 mutual attraction of Caloric and Caoutchouc ; 

 the former of which penetrates the latter, and 

 pervades every part of it with the greatest ease 

 and expedition ; by which the resin is com- 

 pelled to accommodate its pores to that 

 portion of the Calorific fluid which is due to 

 its whole mass, at any particular degree of 

 temperature. In order to apply the last re- 

 mark to the phenomenon under consideration 

 I may observe, that if a force be exerted on a 

 piece of Caoutchouc to alter the dimensions of 

 its pores, the mutual attraction mentioned 

 above will resist the effort. But the ease 

 with which tliis substance may be made to 

 change its figure, and tiie retractile power 

 which it possesses on these occasions, shew that 



