THE ELECTRIC RAILWAY. 743 



vicinity of coils of wire, or coils of wire in the vicinity of magnets. 

 The significance of his discovery was so apparent that inventors began 

 at once to devise means for generating currents upon an extended 

 scale, by moving large magnets in the vicinity of large coils of wire 

 by means of machinery ; and this mechanical system has now been 

 brought to such perfection that the cost of producing a horse-power 

 of electrical energy can be as easily and almost as accurately calcu- 

 lated as the cost of producing a horse-power in a steam-engine or any 

 other familiar apparatus. 



In order to arrive at a clear comprehension of the present state of 

 the art, it will be necessary to remember that any work which we per- 

 form must be performed by the expenditure of a certain and absolute 

 amount of energy, and that we can not create this energy, but can only 

 obtain it by changing the form of some other kind of energy. In 

 the voltaic battery, as we have said, the electrical energy is obtained 

 by transforming the heat of the chemical action going on in the cell 

 into electrical energy, so that the amount of the latter that can be 

 got out of any voltaic battery is limited by the amount of energy of 

 the chemical combination. Now, the metal ordinarily used for fur- 

 nishing chemical energy in a voltaic battery is zinc, and the heat of 

 combination of zinc with oxygen is only about one sixth of that of 

 coal, while its cost is more than twenty times as great ; so that, to get 

 the same amount of energy from zinc as from coal, would cost about 

 one hundred and twenty times as much. Now, in the mechanical 

 method of generating electricity, the electrical energy is produced by 

 the mechanical means of moving large magnets near coils of wire ; 

 but the mechanical energy necessary to do this is obtained by the 

 combustion of coal (i. e., the chemical combination of coal with 

 oxygen). 



It would be incorrect, however, to say that we can in this way pro- 

 duce electricity one hundred and twenty times as cheaply as by a bat- 

 tery, because there is an enormous loss in converting the heat of com- 

 bustion of the coal into electricity, whereas the voltaic battery pro- 

 duces the electricity directly. The losses in converting the energy of 

 the combustion of coal into mechanical energy are so prodigious that 

 even a theoretically perfect engine could not get hold of more than 

 from twenty to twenty-five per cent of the total energy in the coal, on 

 account of the loss of the heat ; so that, if an engine (a good one) has 

 an efficiency of eighty per cent, it can not actually convert into work 

 as much as twenty per cent of the total energy in the coal. The loss 

 now in converting this mechanical energy into the electrical energy in 

 the circuit where it is desired may be taken as about fifteen per cent, 

 so that only about from fifteen to seventeen per cent of the total en- 

 ergy of the burning coal may be looked for in the electrical circuit. 

 But, as the original cost of the coal is only yj-g- of that of the zinc fur- 

 nishing an equal amount of energy, we see that the mechanical method 



