HERMANN VON HELMHOLTZ. 711 



mouth later in Berlin. His paper was read to the Physical Society of 

 that city on the 23d of July, 1847. It was too clear, too powerful, and 

 too convincing to be ignored. The line of thought which he had been 

 following has been traced by his own hand. The study of medicine led 

 to the problem of the nature of ^' vital force." He convinced liimselt 

 tbat if— as Stahl had suggested — an animal had the power now of 

 restraining, and now of liberating the activity of mechanical forces, it 

 would be endowed with the power of perpetual motion. This led to the 

 question whether i)erpetual motion was consistent with what was known 

 of natural agencies. The essay on the Conservation of Force was, 

 according to Yon Helmholtz himself, intended to be a critical investiga- 

 tion and arrangement of the facts which bear on this point for the 

 benefit of x)hysiologists. In form, however, it was addressed to the 

 physicists. 



The paper was called Ueber die Brhaltung der Kraft, eine physika- 

 lische Abhandlung. It opens with the statement, "Vorliegende 

 Abhandlung musste ihrem Hauptinhalte nach hauptsachlich fiir Phy- 

 siker bestimmt werden." It was communicated to the Physical Society 

 of Berlin. The author appears to have expected that it would there 

 be received as a mere summary of accepted facts, and to have hoped 

 that, having gained this authoritative sanction, he could thereafter 

 appeal with greater force to his brother physiologists. To his surprise 

 the physicists were not only interested, but showed a strong disposition 

 to treat the essay as a fantastic speculation. The editor of Poggendorff's 

 Annalen declined to publish it. On the other hand, Helmholtz Avas 

 supported by his fellow-student, Du Bois Reymond, and by mathema 

 ticiau Karl Jacobi. In the eml they carried the Physical Society with 

 them. 



The essay itself is full of interest. The phraseology differs from that 

 we employ, but the use of terms now regarded as archaic is not due to 

 any mistiness of perception. Write energy here and there for "force," 

 potential energy for "tension," as defined in the essay, assume our 

 fuller knowledge of the results of experiment, and the whole might 

 have been written yesterday, instead of nearly fifty years ago. 



The author began by an argument which practically amounts to the 

 statement that science is limited to the search for a mechanical expla- 

 nation of nature, and that, whatever the final result of the quest may 

 be, it must be pushed as far as possible. 



Assuming that the basis of a mechanical theory must ultimately be 

 the action of forces between material iioints, and, implicitly assuming 

 the Newtonian laws of motion, the conclusion is reached that the law 

 of the conservation of energy holds good, and holds good only if the 

 forces are central; that is, if they are attractions or repulsions, the 

 magnitudes of which depend solely on the distances between the mutu- 

 ally reacting pai'ticles. 



The cogency of this as an a priori })roof of the conservation of energy 



