ARMY SURGEON AT POTSDAM 45 



which cannot in any wise be added to or subtracted from: 

 the quantity of energy in inorganic nature is as eternal and 

 unalterable as the quantity of matter/ the constancy of which 

 had been established as a fundamental law of chemistry by- 

 Lavoisier half a century before. 



Helmholtz termed this universal principle, now known as 

 the Law of the Conservation of Energy, the Law of the 

 Conservation of Force; it asserts that each transformation 

 of energy takes place under exactly measurable quantitative 

 relations, whether the form of energy be the vis viva of motion, 

 or electrical and magnetic energy, or heat, whence again the 

 impossibility of perpetual motion follows. 



In order to include within the scope of his considerations 

 such natural forces as may be still unknown, he affirms with 

 the care of a great investigator that the validity of the law of 

 the constancy of the sum of vis viva and of what he called the 

 'tensional forces', i.e. of actual and potential energy, is in the 

 highest degree probable, since it contradicts none of the known 

 facts of science, and is on the contrary confirmed by many of 

 these in the most striking manner. He tests the energy- 

 equivalents of heat, of electrical action, of magnetism and 

 electro-magnetism, and after finding the law to be universally 

 valid, turns as physiologist to the natural processes of organic 

 existence, and shows that the problem of the conservation 

 of energy is here a question of whether the oxidation and 

 metabolism of the nutritive substances generate an equivalent 

 quantity of heat to that given off by animals, a problem which 

 had already occupied him for some months in Potsdam. 



' I have endeavoured/ he says at the close of this masterly 

 treatise, l to state in the most complete manner possible the 

 inferences which flow from a combination of the law with 

 other known laws of natural phenomena, and which still await 

 their experimental proof. The object of this investigation was 

 to lay before physicists as fully as possible the theoretic and 

 practical importance of a law whose complete corroboration 

 must be regarded as one of the principal problems of the 

 natural philosophy of the future/ 



At the time when Helmholtz began his analytical study of 

 the natural sciences, the law of the persistence of matter 

 (by which the elements may alter in regard to the mode of 



