430 FEAGMENTS OF SCIENCE. 



1842 wrote to Liebig, asking him to 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 * An- 

 nalen ' 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 inor- 

 ganic nature. He finds in the universe two systems of 

 causes which are not mutually convertible; the dif- 

 ferent kinds of matter and the different forms of force. 

 The first quality of both he affirms to be indestructi- 

 bility. A force cannot become nothing, nor can it arise 

 from nothing. Forces are convertible but not de- 

 structible. In the terminology of his time, he then 

 gives clear expression 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 actually 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? Ex- 

 periment alone, says Mayer, can help us here. He 

 warms water by stirring it; he refers to the force ex- 

 pended 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.' 



