OBTAINS EQUIVALENT BY FRICTION. 7 1 



called the Conservation of Energy as the result of his dis- 

 coveries. This postscript, which was added in August to 

 his paper of the 23rd of July, is as follows : — 



P.S. — " We shall be obliged to admit that Count 

 Rumford was right in attributing the heat evolved by 

 boring a cannon to friction and not (in any considerable 

 degree) to any change in the capacity of the metal. I have 

 proved experimentally that heat is evolved by the passage 

 of water through narrow tubes. My apparatus consisted 

 of a piston perforated by a number of small holes working 

 in a cylindrical glass jar containing 7 lb. of water. I thus 

 obtained one degree of heat per lb. of water from a 

 mechanical force capable of raising about 770 lb. to the 

 height of one foot, a result which will be allowed to be very 

 strongly confirmatory of our previous deductions. I shall 

 lose no time in repeating and extending these experiments, 

 being satisfied that the grand agents of nature are by the 

 Creator's flat indestructible, and that whatever mechanical 

 force is expended an exact equivalent of heat is always 

 obtained. 



" On conversing a few days ago with my friend, Mr. 

 John Davies, he told me that he had himself, a few years 

 ago, attempted to account for that part of animal heat 

 which Crawford's theory had left unexplained by the 

 friction of the blood in the veins and arteries, but that 

 finding a similar hypothesis in Haller's " Physiology " he had 

 not pursued the subject further. It is unquestionable that 

 heat is produced by such friction, but it must be understood 

 that the mechanical force expended in the friction is a part 

 of the cause of the affinity which causes the venous blood 

 to unite with oxygen ; so that the whole heat of the system 

 must still be referred to chemical changes. But if the 



