1861.] Professor Helmholtz on the Conservation of Force. 347 



WEEKLY EVENING MEETING, 



Friday, April 12, 1861. 



William Robert Grove, Esq. M.A. Q.C. F.R.S. Vice-President, 



in the Chair. 



Professor Helmholtz, F.R.S. 



On the Application of the Law of the Conservation of Force to 

 Organic Nature. 



The most important progress in natural philosophy by which the 

 present century is distinguished, has been the discovery of a general 

 law which embraces and rules all the various branches of physics and 

 chemistry. This law is of as much importance for the highest specula- 

 tions on the nature of forces, as for immediate and practical questions 

 in the construction of machines. This law at present is commonly 

 known by the name of " the principle of conservation of force." It 

 might be better perhaps to call it, with Mr. Rankine, " the conservation 

 of energy," because it does not relate to that which we call commonly 

 intensity of force ; it does not mean that the intensity of the natural 

 forces is constant : but it relates more to the whole amount of power 

 which can be gained by any natural process, and by which a certain 

 amount of work can be done. For example : if we apply this law to 

 gravity, it does not mean, what is strictly and undoubtedly true, that 

 the intensity of the gravity of any given body is the same as often as 

 the body is brought back to the same distance from the centre of the 

 earth. Or with regard to the other elementary forces of nature — for 

 example, chemical force : when two chemical elements come together, 

 so that they influence each other, either from a distance or by imme- 

 diate contact, they will always exert the same force upon each other — 

 the same force both in intensity and in its direction and in its quantity. 

 This other law indeed is true ; but it is not the same as the principle 

 of conservation of force. We may express the meaning of the law of 

 conservation of force by saying, that every force of nature when it 

 effects any alteration, loses and exhausts its faculty to effect the same 

 alteration a second time. But while, by every alteration in nature, that 

 force which has been the cause of this alteration is exhausted, there is 

 always another force which gains as much power of producing new 

 alterations in nature as the first has lost. Although, therefore, it is 

 the nature of all inorganic forces to become exhausted by their own 

 working, the power of the whole system in which these alterations 

 take place is neither exhausted nor increased in quantity, but only 



