THE PROGRESS OF PHYSICS. 143 



which the caloric theory received was dealt it by Ben- 

 jamin Thompson, better known as Count Rumford, 

 who published his observations on the boring of can- 

 non at Munich in 1798. Surprised at the amount of 

 heat given off in the operation, he determined to 

 measure this by its effect in raising the temperature 

 of surrounding water. "At the end of two hours 

 and thirty minutes the water actually boiled ! " and 

 Count Rumford argued : " It is hardly necessary to 

 add that anything which an insulated body, or system 

 of bodies, can continue to furnish without limitation, 

 cannot possibly be a material substance, and it ap- 

 pears to me to be extremely difficult, if not impossible 

 to form any distinct idea of anything capable of being 

 excited and communicated in the manner in which 

 heat was excited and communicated in these experi- 

 ments, except it be motion." 



The supporters of the idea that heat is a material 

 substance argued that the production of heat by fric- 

 tion or abrasion was due to the fact that the fragmen- 

 tation of the body diminished its capacity for holding 

 caloric; and if, as Prof. Tait points out, Rumford 

 had seen his way to a satisfactory experiment "which 

 would have tested the capacity for heat of the abraded 

 metal and of the metal before abrasion, then the fact 

 that heat is not matter would have been established. 

 But the essential experiment most readily a chem- 

 ical one did not suggest itself, and this is in part the 

 reason why Rumford's experiments published in 1798 

 were but little noticed until about 1840. 



Rumford's argument was on the main line of prog- 

 ress, but his measurement of the heat evolved by fric- 

 tion was rough, and he was unable to make a definite 

 comparison between the energy expended and the 

 work done and the heat dissipated. 



