358 A SHORT HISTORY OF SCIENCE 



they require to be confirmed by further experiments. The aim of this 

 investigation, and what must excuse me likewise for its hypothetical 

 sections, was to explain to natural philosophers the theoretical and 

 practical importance of the law, the complete verification of which 

 may well be looked upon as one of the main problems of physical 

 science in the near future. 



Fifteen years later Helmholtz spoke of the principle as follows : 

 The last decades of scientific development have led us to the recogni- 

 tion of a new universal law of all natural phenomena, which, from its 

 extraordinarily extended range, and from the connection which it 

 constitutes between natural phenomena of all kinds, even of the 

 remotest times and the most distant places, is especially fitted to give 

 us an idea of what I have described as the character of the natural 

 sciences, which I have chosen as the subject of this lecture. This law 

 is the Law of the Conservation of Force, a term the meaning of which 

 I must first explain. It is not absolutely new ; for individual domains 

 of natural phenomena it was enunciated by Newton and Daniel 

 Bernoulli; and Rumford and Humphry Davy have recognised dis- 

 tinct features of its presence in the laws of heat. The possibility 

 that it was of universal application was first stated by Mayer in 1842, 

 while almost simultaneously with, and independently of him, Joule 

 made a series of important and difficult experiments on the relation 

 of heat to mechanical force, which supplied the chief points in which 

 the comparison of the new theory with experience was still wanting. 

 The law in question asserts, that the quantity of force which can be 

 brought into action in the whole of Nature is unchangeable, and can neither 

 be increased nor diminished. 



This doctrine is now so fundamental and so familiar as to require 

 no further comment. The indestructibility of matter had already 

 become axiomatic. Henceforth, energy also was to be considered 

 constant and indestructible. 



DISSIPATION OF ENERGY. It remained for William Thomson 

 (Lord Kelvin), applying the principle of the conservation of energy 

 to the thermodynamic laws of Carnot, to deduce the other great 

 principle of the Dissipation of Energy, which recognizes that 

 while total energy is constant, useful energy is diminishing by the 

 continual degeneration of other forms into non-useful or dis- 



