332 THE POPULAR SCIENCE MONTHLY. 



To determine, therefore, upon this last alternative, he performed 

 the following experiment : 



A block of ice, having a small channel cut around its upper edge, 

 was placed under the receiver of an air-pump. The channel was 

 filled with water, and upon the block, though not in contact with the 

 water, was also placed a clock-work so contrived that one of the ex- 

 ternal wheels of its machinery came in contact with a thin metal 

 plate. By the friction between these surfaces a considerable amount 

 of heat could be produced, which might be made to melt wax, tallow, 

 or any similar substance fusible at the temperature which could be 

 thus produced. 



The receiver, previously filled with carbonic-acid gas, was next 

 exhausted as completely as possible by the air-pump and absorption 

 by caustic potash ; upon then setting the machine to work the wax 

 was melted rapidly, and the temperature of the whole apparatus in- 

 creased by more than 1 Fahr., thus proving the excitation of heat 

 under the conditions imposed. 



Consistently with the remaining supposition the third it was 

 then only to be inferred that caloric had been collected from the 

 bodies in contact. Neglecting, however, the vapor of water which 

 formed the rarefied atmosphere within the receiver, the only other 

 body in contact with the apparatus was the ice. But against the as- 

 sumption of this latter having furnished any heat, Davy here drew at- 

 tention to the water still remaining liquid in the canal, and which pre- 

 sumably would have been frozen had the ice parted with any heat. 



It is easy to perceive that such a course of reasoning was neither 

 exhaustive with respect to the non-existence of caloric, nor conclusive 

 as to the dynamic character of heat. For, had he even been success- 

 ful in demolishing the doctrine of caloric, the simple refutation of one 

 physical hypothesis could never have been construed into more than 

 an increase in probability of all those opposed to it ; and in this in- 

 stance, perhaps no considerations would have been accepted as con- 

 clusive by the materialists, w T hich, failing to experimentally establish 

 the true nature of heat, should still have left their favorite notion 

 open to any modification, however artificial, which might reconcile it 

 in the least degree with facts which would be doubted and distorted 

 in the interest of these preconceived opinions. 



Heat being only a particular phase of energy, it was necessary and 

 sufficient to show, as done by Rumford, with respect to its frictional 

 excitation, that its production depended only on the expenditure of 

 energy implied in its inexhaustibility and always in the same de- 

 gree, as he proved by special determinations. 1 It was the subsequent 



1 Professors Tait and Balfour Stewart are authority for the statement that " Rumford 

 pointed out other methods to be employed in determining the amount of heat produced 

 by the expenditure of mechanical power, instancing particularly the agitation of water 

 or other liquids, as in churning." (Tait's " Historical Sketch," p. 1 ; Stewart's " Element- 

 ary Treatise on Heat," p. 307.) 



