THE COPLEY MEDALIST OF 1871. 483 



publish in his ' Annalen ' a brief preliminary notice of 

 the work then accomplished. Liebig did so, and Dr. 

 Mayer's first paper is contained in the May number of 

 the 'Annalen' for 1842. 



Mayer had reached his conclusions by reflecting on 

 the complex processes of the living body ; but his first 

 step in public was to state definitely the physical prin- 

 ciples on which his physiological deductions were to 

 rest. He begins, therefore, with the forces of inorganic 

 nature. He finds in the universe two systems of causes 

 which are not mutually convertible ; the different kinds 

 of matter and the different forms of force. The fir^t 

 quality of both he affirms to be indestructibility. A 

 force cannot become nothing, nor can it arise from 

 nothing. Forces are convertible but not destructible. 

 In the terminology of his time, he then gives clear ex- 

 pression to the ideas of potential and dynamic energy, 

 illustrating his point by a weight resting upon the 

 earth, suspended at a height above the earth, and actu- 

 ally falling to the earth. He next fixes his attention 

 on cases where motion is apparently destroyed, without 

 producing other motion ; on the shock of inelastic 

 bodies, for example. Under what form does the vanished 

 motion maintain itself ? Experiment alone, says Mayer, 

 can help us here. He warms water by stirring it ; he 

 refers to the force expended in overcoming friction. 

 Motion in both cases disappears ; but heat is generated, 

 and the quantity generated is the equivalent of the 

 motion destroyed. ' Our locomotives,' he observes with 

 extraordinary sagacity, ' may be compared to distilling 

 apparatus : the heat beneath the boiler passes into the 

 motion of the train, and is again deposited as heat in 

 the axles and wheels.' 



A numerical solution of the relation between heat 

 and work was what Mayer aimed at, and towards the end 



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