Caoutchouc 07'' Indian Rnbter, 2P1 



for accuracy, will not trust his own sense of 

 feeling in inquiries of this description, but will 

 contrive to employ a Thermometer in the bu- 

 siness. Should the objection be started, the 

 answer to it is obvious ; for the experiment in 

 its present state denlonstrates the reality of a 

 singular fact ; by convincing that sense, which 

 is the only direct judge in the case, that the 

 temperature of a piece of Caoutchouc may be 

 changed, by compelling it to- change its di- 

 mensions. The use of a Thermometer deter 

 mines the relative magnitudes of these vari- 

 ations, by referring the question of temper- 

 ature to the eye ; experiments of this sort are 

 therefore of a mathematical nature, and afford 

 a kind of knowledge with which we have 

 nothing to do at present ; for we are not in- 

 quiring after proportions, but endeavouring to 

 establish the certainty of a fact, which may 

 assist in discovering, the reason of the uncom- 

 mon elasticity observable in Caoutchouc. My 

 essay or letter appears to be running into a 

 long digression ; the subject must therefore be 

 resumed, and it will not be improper to 

 premise the following simple experiment, in 

 the present state of the inquiry ; because it 

 seems capable of affording no inconsiderable 

 dcirrcc of insi<rht into the plan, wliich natiii\* 



O v> I 



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