ON THE CONSERVATION OF FORCE. 279 



It is not to be denied that, in the natural sciences, this kind 

 of interest is wanting. Each individual fact, taken by itself, 

 can indeed arouse our curiosity or our astonishment, or be useful 

 to us in its practical applications. But intellectual satisfaction 

 we obtain only from a connection of the whole, just from its 

 conformity with law. Reason we call that faculty innate in us 

 of discovering laws and applying them with thought. For the 

 unfolding of the peculiar forces of pure reason in their entire 

 certainty and in their entire bearing, there is no more suitable 

 arena than inquiry into Nature in the wider sense, the mathe- 

 matics included. And it is not only the pleasure at the successful 

 activity of one of our most essential mental powers , and the vie- 

 torious subjections to the power of our thought and will of an 

 external world, partly unfamiliar, and partly hostile, which is the 

 reward of this labour ; but there is a kind, I might almost say, 

 of artistic satisfaction, when we are able to survey the enormous 

 wealth of Nature as a regularly-ordered whole a kosmos, an 

 image of the logical thought of our own mind. 



The last decades of scientific development have led us to the 

 recognition 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 de- 

 scribed 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 oj 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 distinct features of its presence 

 in the laws of heat. 



The possibility that it was of universal application was 

 first stated by Dr. Julius Robert Mayer, a Schwabian physician 

 (now living in Heilbronn), in the year 1842, while almost 

 simultaneously with, and independently of him, James Prescot 

 Joule, an English manufacturer, made a series of important and 



