PROPERTY OF INDIAN RVBBER. <^Q'1 



blifli the certainty of a fa6t, which may affift in difcovering 

 the reafon of the uncommon elafticity obfervable in Caout- 

 chouc. My elTay or letter appears to be running into a long 

 digreffion; the fubjedl mud therefore be refumed, and it will 

 not be improper to premife the following fimple experiment, 

 in the prefent ftate of the inquiry ; becaufe it feems capable 

 of affording no inconfiderable degree of infight into the 

 plan which nature purfues in producing the phenomenon in 

 queftion. 



Fxp. 2. If one end of a (lip of Caoutchouc be fattened to CMutchouc 

 a rod of metal or wood, and a weight be fixed to the other when ftretched 

 extremity, in order to keep it in a vertical pofition; the ^J^^"^']^^^^^.^'^^^ 

 thong will be found to become fliorfer wilh heat and longer Ly cold. 

 with cold. The procetTes of heating, cooling, and meafuring 

 bodies are fo well known, that I need not enter into the mi- 

 nuter parts of the experiment ; it will be proper, however, 

 to add, that an increafe of temperature diminifhes the fpe- 

 cific gravity of the Indian Rubber, and a lofs of heat occa- 

 Hons a contrary effeft in it ; as 1 have proved experimentally. 

 The knowledge of the latter fa6t leads me to conclude, ap- 

 parently on rcafonable grounds, that the pores or intcrftices 

 of Caoutchouc are enlarged by heat, and dimlniflied by cold; 

 confequently when a flip of this fubflance which remains ex- 

 tended by a weight, or the application of force, happens to 

 contrail from an acceffion of temperature, the capacity of 

 its pores, taken feparately or colle6lively, is augmented by 

 the change that fakes place^in the figure of the thong. Now ^, _, ,. 



if the exigence of caloric be admitted, it will follow from this fubHance : 



the preceding arguraenls, that the phenomenon under con- '* ," . ^^"^ ^y 

 /-J • ■ ^ • • t 1 T /• • I -rr- caloric, as ropes 



lideration is occahoned by the alternate ablorption and emiilion are by water • 



of the calorific fluid, iiPthe fame manner that ropes, the 

 blades of Fuci, as well as many more bodies, are obliged to 

 contrafl and extend themfelves, by the alternate abforption 

 and emiffion of water. — You will perceive by the tenour of 

 i the foregoing obfervalions, that my theory of this cafe of 

 elafticity is perfectly mechanical j in fa£t, the explanation of 

 it depends upon the mutual attraftion of Caloric and Caout- 

 chouc; the former of which penetrates the latter, and pervades 

 j every part of it with the greateft eafe and expedition ; by 

 \ which the refin is compelled to accommodate its pores to that 

 I portion of the Calorific fluid which is due to its whole mafs, 



at 



