MAYER 277 



force (energy) is a constant quantity.' Only the form of 

 energy is changed; its quantity remains unchanged. 'There 

 is in truth only one single force (energy). In eternal change 

 this circulates in dead as in living nature. In both no pro- 

 cess takes place without change of form of the force (energy).' 

 Mayer then gives twenty-five pertinent examples of energy 

 transformations, or changes of position of energy, the quan- 

 tity remaining the same, which, after what has been just said 

 with equal impressiveness concerning the different forms of 

 energy, cannot leave the slightest doubt in anyone who has 

 even glanced through this essay and is sufficiently prepared 

 by his own thought, concerning the sense and extent of 

 Mayer's achievement. 



Mayer continues with an extensive discussion on energy 

 of relationship in living nature, in which he as a doctor took 

 a particular interest.^ Here again he starts from the highest 

 point of view, beginning with the energy of the sun, which 

 pours upon the earth in the form of light, and here, besides 

 warmth and raising of water to the clouds, also produces the 

 chemical energy of plants, and hence that of animals. It is 

 also important that he clearly and distinctly points out that 

 in muscular work there is a direct transformation of the 

 chemical energy of food into mechanical (potential or 

 kinetic) energy, without the intermediary of heat energy, 

 which is required by the steam engine. 



It is obvious that this magnificent structure of ideas, 

 which this simple doctor had developed in the course of a 

 number of years, at first could only be hypothesis or sup- 

 position, and could only gradually become transformed into 

 tried and tested knowledge after many quantitative com- 

 parisons had been made with reality. This transformation - 

 to which Joule at once greatly contributed - has been com- 

 pleted to-day, and has not changed anything of importance 



^ The title of the essay already puts this part in the forefront, after the 

 first paper had been limited to forces of non-living nature. 



