236 THE EIDDLE OF THE UNIVERSE. 



prove by an accurate measurement that not a single 

 particle of energy is lost in the process. 



The sum-total of force or energy in the universe 

 remains constant, no matter what changes take place 

 around us ; it is eternal and infinite, like the matter 

 on which it is inseparably dependent. The whole 

 drama of nature apparently consists in an alternation 

 of movement and repose ; yet the bodies at rest have 

 an inalienable quantity of force, just as truly as those 

 that are in motion. It is in this movement that the 

 potential energy of the former is converted into the 

 kinetic energy of the latter. " As the principle of 

 the persistence of force takes into account repulsion 

 as well as attraction, it affirms that the mechanical 

 value of the potential energy and the kinetic energy 

 in the material world is a constant quantity. To put 

 it briefly, the force of the universe is divided into two 

 parts, which may be mutually converted, according to 

 a fixed relation of value. The diminution of the one 

 involves the increase of the other ; the total value 

 remains unchanged in the universe." The potential 

 energy and the actual, or kinetic, energy are being 

 continually transformed from one condition to the 

 other ; but the infinite sum of force in the world at 

 large never suffers the slightest curtailment. 



Once modern physics had established the law of 

 substance as far as the simpler relations of inorganic 

 bodies are concerned, physiology took up the story, 

 and proved its application to the entire province of 

 the organic world. It showed that all the vital 

 activities of the organism — without exception — are 

 based on a constant " reciprocity of force " and a 

 correlative change of material, or metabolism, just as 

 much as the simplest processes in " lifeless " bodies. 



