ON THE CONSEEVATION OF FORCE. 315 



We might also drive a magneto-electrical machine by a falling 

 weight; it would then furnish electrical currents. 



We have seen that chemical forces, when they come into 

 play, produce either heat or electrical currents or mechanical 

 work. 



We have seen that heat may be changed into work ; there 

 are apparatus (thermo-electric batteries) in which electrical cur- 

 rents are produced by it. Heat can directly separate chemical 

 compounds ; thus, when we burn limestone, it separates carbonic 

 acid from lime. 



Thus, whenever the capacity for work of one natural force 

 is destroyed, it is transformed into another kind of activity. 

 Even within the circuit of inorganic natural forces, we can 

 transform each of them into an active condition by the aid of 

 any other natural force which is capable of work. The connec- 

 tions between the various natural forces which modern physics 

 has revealed, are so extraordinarily numerous that several 

 entirely different methods may be discovered for each of these 

 problems. 



I have stated how we are accustomed to measure mechanical 

 work, and how the equivalent in work of heat may be found. 

 The equivalent in work of chemical processes is again measured 

 by the heat which they produce. By similar relations, the 

 equivalent in work of the other natural forces may be expressed 

 in terms of mechanical work. 



If, now, a certain quantity of mechanical work is lost, there 

 is obtained, as experiments made with the object of determining 

 this point show, an equivalent quantity of heat, or, instead of 

 this, of chemical force ; and, conversely, when heat is lost, we 

 gain an equivalent quantity of chemical or mechanical force ; 

 and, again, when chemical force disappears, an equivalent of 

 heat or work ; so that in all these interchanges between various 

 inorganic natural forces working force may indeed disappear 

 in one form, but then it reappears in exactly equivalent 

 quantity in some other form ; it is thus neither increased nor di- 

 minished, but always remains in exactly the same quantity. 

 We shall subsequently see that the same law holds good also 



