292 A Description of a Property of 



pursues in producing the phenomenon in 

 question. 



EXPERIMENT 2. 



If one end of a slip of Caoutchouc be fas- 

 tened to a rod of rnetal or wood, and a weight 

 be fixed to the other extremity, in order to 

 keep it in a vertical position ; the thong will 

 be found to become shorter with heat and 

 longer w^ith cold. The processes of heating, 

 cooling, and measuring bodies are so well 

 known, that I need not enter into the minuter 

 parts of the experiment ; it will be proper 

 however to add, that an increase of tempe- 

 raturc diminishes the specific gravity of the 

 Indian Rubber, and a loss of heat occasions a 

 contrary effect in it ; as I have proved experi- 

 menially. The knowledge of the latter fact 

 leads me to conclude, apparently on reason- 

 able grounds, that the pores or interstices of 

 Caoutchouc are enlarged by heat, and dimi- 

 nished by co.ld ; consequently when a slip of 

 this substance which remains extended by a 

 weight, or the application of force, happens 

 to contract from an accession of temperature, 

 the capacity of its pores, taken separately or 

 collectively, is augmented by the change that 



