SCIENCE AND MAN. 345 



amount of energy can assume while maintaining un- 

 varying quantitative stability. When that form of 

 power which we call an electric current passes through 

 Grove's battery, zinc is consumed in acidulated water ; 

 and in the battery we are able so to arrange matters 

 that when no current passes no zinc shall be consumed. 

 Now the current, whatever it may be, possesses the 

 power of generating heat outside the battery. We can 

 fuse with it iridium, the most refractory of metals, or 

 we can produce with it the dazzling electric light, and 

 that at any terrestrial distance from the battery itself. 



We will now, however, content oiu*selves with caus- 

 ing the current to raise a given length of platinum wire, 

 first to a blood-heat, then to redness, and finally to a 

 white heat. The heat under these circumstances gene- 

 rated in the battery by the combustion of a fixed 

 quantity of zinc is no longer constant, but it varies in- 

 versely as the heat generated outside. If the outside heat 

 be nil, the inside heat is a maximum ; if the external 

 wire be raised to a blood-heat, the internal heat falls 

 slightly short of the maximum. If the wire be rendered 

 red-hot, the quantity of missing heat within the battery 

 is greater, and if the external wire be rendered white-hot, 

 the defect is greater still. Add together the internal 

 and external heat produced by the combustion of a 

 given weight of zinc, and you have an absolutely con- 

 stant total. The heat generated without is so much 

 lost within, the heat generated within is so much lost 

 without, the polar changes already adverted to coming 

 here conspicuously into play. Thus in a variety of 

 ways we can distribute the items of a never- varying sum, 

 but even the subtle agency of the electric current places 

 no creative power in our hands. 



Instead of generating external heat, we may cause 

 the current to effect chemical decomposition at a dis- 



