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known as Count Rum ford, was the first to give 

 scientific reason for rejecting the hypothesis of 

 caloric and accepting the theory that heat is a mode 

 of motion. Rumford had made experiments on the 

 quantity of heat given off by bcdies as the result 

 of friction, and had not been able to find a limiting 

 value of this quantity. His deduction therefrom is 

 given in these words : " Anything which any in- 

 sulated body, or system of bodies, can continue 

 to furnish without limitation cannot possibly be a 

 material substance ; and it appears to be extremely 

 difficult, if not impossible, to form any distinct idea 

 of anything being excited and communicated in the 

 manner that heat was excited and communicated, 

 except it be motion." This is a definite statement 

 by a competent authority that the grounds on which 

 he adopted the dynamical theory of heat, and re- 

 jected the caloric theory, were the very grounds on 

 which I am endeavouring to show that all scientific 

 theories are respectively accepted or rejected. The 

 direct arguments for the dynamical theory of heat 

 are, to this day, based upon experiments similar in 

 character to those of Rumford, and, as far as I am 

 able to learn, no scientific writer has ever impugned 

 the sufficiency of the argument which Rumford 

 used. 



Here we have three typical instances in each of 

 which one scientific theory has been rejected and 

 another accepted. In two of them we have the 



