ATM AND PROGRESS OF PHYSICAL SCIENCE. 333 



height of 425 metres. If we convert work into heat by friction 

 we again use, in heating a given weight of water one degree 

 Centigrade, the motive force which the same quantity of water 

 would have generated in flowing down from a height of 425 

 metres. Chemical processes generate heat in definite proportion, 

 and in like manner we estimate the motive power equivalent to 

 such chemical forces ; and thus the energy of the chemical force 

 of affinity is also measurable by the mechanical standard. The 

 same holds true for all the other forms of natural forces, but it 

 will not be necessary to pursue the subject further here. 



It has actually been established, then, as a result of these 

 investigations, that all the forces of nature are measurable by 

 the same mechanical standard, and that all pure motive forces 

 are, as regards performance of work, equivalent. And thus 

 one great step towards the solution of the comprehensive 

 theoretical task of referring all natural phenomena to motion 

 has been accomplished. 



Whilst the foregoing considerations chiefly seek to elucidate 

 the logical value of the law of the conservation of force, its 

 actual signification in the general conception of the processes of 

 nature is expressed in the grand connection which it establishes 

 between the entire processes of the universe, through all dis- 

 tances of place or time. The universe appears, according to 

 this law, to be endowed with a store of energy which, through 

 all the varied changes in natural processes, can neither be 

 increased nor diminished, which is maintained therein in ever- 

 varying phases, but, like matter itself, is from eternity to 

 eternity of unchanging magnitude: acting in space, but not 

 divisible, as matter is, with it. Every change in the world 

 simply consists in a variation in the mode of appearance of this 

 store of energy. Here we find one portion of it as the vis viva of 

 moving bodies, there as regular oscillation in light and sound ; 

 or, again, as heat, that is to say, the irregular motion of in- 

 visible particles; at another point the energy appears in the 

 form of the weight of two masses gravitating towards each 

 other, then as internal tension and pressure of elastic bodies, or 

 as chemical attraction, electrical tension, or magnetic distri- 



