COUNT RUMFOKD. 173 



all directions, without interruption or intermission, and 

 without any signs of diminution or exhaustion. In 

 reasoning on this subject, we must not forget that most 

 remarkable circumstance, that the source of the heat 

 generated by friction in these experiments appeared 

 evidently to be inexhaustible. It is hardly necessary 

 to add that anything which any insulated body or 

 system of bodies can continue to furnish without limi- 

 tation cannot possibly be a material substance ; and it 

 appears to me to be extremely difficult, if not quite 

 impossible, to form any distinct idea of anything capa- 

 ble of being excited and communicated in those expe- 

 riments, except it be Motion.' l 



1 Heat a Mode of Motion, Lecture II. 



