492 PEESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 



It was now but natural to examine whether there were not a definite, 

 calculable relation between the conversion of the entire visible motion 

 of the frictional mass into that invisible motion of the ultimate mole- 

 cules, *. e. its transformation into heat. Rurnford himself had made the 

 experiment of such an estimate of the mechanical value of the increase 

 of the temperature of a given quantity for each therinometrical degree. 

 At that time, however, the scientific conception of " work " had not as 

 yet found a place in mechanics; therefore an exact definition was only 

 X>ossible at a later period. It came almost simultaneously from Dr. 

 Julius Robert Mayer (May 1842-1851) and James Prescott Joule (August 

 1843-1819). The former was a practicing physician in Heilbronn, the 

 latter a physicist in Manchester, thoroughly conversant with practical 

 mechanics. Mayer took up this subject mainly from a theoretical 

 point of view, and verified his ingenious conclusions by experiments. 

 Joule took the opposite direction. Both happily arrived, in a strik- 

 ing manner, at the great object; the former more powerful in fertile, 

 logical ideas, the latter stronger in the province of experiment, and 

 for this reason, more accurate in the final determination of numerical 

 results. We will attach ourselves to Joule, as far as the experi- 

 mental part of this subject is concerned, well aware that the honor 

 of originating this highly important matter is almost generally con- 

 ceded to Dr. Mayer, who has now passed away. We say " almost 

 generally," because recently the priority of Mayer in this important 

 matter has been disputed on several sides, particularly by some Eng- 

 lish physicists. Attention was called to the fact that Mohr, in his 

 "Ideas on the nature of heat" (1837), that is five years earlier tban 

 Mayer, had advanced as far as the latter, that also Seguin (1839), Fara- 

 day (1839), and Liebig (1841) had approached earlier than Mayer the 

 theory of the transformation of heat into mechanical power. Atten- 

 tion was especially directed to " Essays on Force," by Colding, which 

 appeared in the Danish language in the year 1843, in which the author 

 asserted, a priori the imperishability of natural forces and their trans- 

 formation into equivalents of the other forces ; and (by his own state- 

 ment) he had conceived these ideas four years before on the ground of 

 dAlembert's theorem, of " The active and inert forces." 



Finally Joule was put in opposition to Mayer. The relation of the 

 labors of the two last named has been indicated above. In whichever 

 way the question of priority may be decided, it is certain that only 

 Mayer and Joule have successfully grappled with this problem, and that 

 Mayer is by almost general consent celebrated as the first discoverer of 

 the calculable transformation of mechanical work into heat. Indeed, 

 according to existing records, no one before him recognized and pro- 

 claimed this great truth so plainly and clearly, and no one before him 

 made such far-reaching application of the consequences as he did. 



For reasons above referred to, we have decided on the discussion of 

 Joule's experiments, which have their appropriate place here, and of the 



