THE CONSERVATION OF FORCE 183 



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 mathematics included. And it is not 

 only the pleasure at the successful activity of one of our 

 most essential mental powers; and the victorious 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 enor- 

 mous wealth of Nature as a regularly-ordered whole a kos- 

 mos, 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 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 abso- 

 lutely 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 physi- 

 cian (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 difficult experiments on the relation of heat 

 to mechanical force, which supplied the chief points in 



