1 8 THE MEASURE OF MECHANICAL EFFECT. 



mechanical and commercial measure of potency, and under 

 the names of 'work' and 'accumulated work/ these men 

 had become familiar with what are now known as 'work' and 

 'energy' (actual and potential). But in so far as 'work' was 

 spent in overcoming friction, it was rightly considered as 

 the measure of mechanical power annihilated. 



Heat had been recognized as a measurable quantity, 



expressed by product of the weight of water multiplied by 



the rise of temperature effected by the heat. The discoveries 



of Black and Watt had led to the recognition of something 



in heat other than that which merely went to raise the 



temperature of matter, a recognition expressed in the term 



caloric, invented by Lavoisier (1787), for the imponderable 



fluid which imparted elasticity and temperature to matter, 



and which in Lavoisier's view might be vis viva. But 



suggestive, as this recognition undoubtedly was, to those 



physical philosophers who directed their philosophy to the 



subject, the orthodox school still maintained, as a dogma, 



the materiality of heat, and ignoring Lavoisier's reservation 



as to the materiality of caloric, continued to regard heat as 



unchangeable, like a definite form of matter, accepting all 



the physical casuistry which had been invented in order to 



reconcile this dogma with observed phenomena. That the 



development of heat by friction between bodies in relative 



motion was evidence that sensible heat consisted of some 



form of mechanical activity, set up by the action between 



the bodies, had been borne in upon the minds of philosophers 



from very early times, and particularly during the previous 



200 years. This view, however, had come to be regarded 



as opposed to the dogma of caloric by those who held it as 



well as by the orthodox school {See Appendix) ; the idea 



of the materiality of heat associated with the dogma 



