430 FRAGMENTS OF SCIENCE. 



wire. When the handle of the machine is rapidly 

 turned the wire glows, first with a red heat, then with 

 a white heat, and finally with the heat of fusion. The 

 moment the wire melts, the circuit round the armature 

 is broken, an instant relief from the labour thrown upon 

 the arm being the consequence. Clearly realise the 

 equivalent of the heat here developed. During the 

 period of turning the machine a certain amount of 

 combustible substance was oxidised or burnt in the 

 muscles of my arm. Had it done no external work, 

 the matter consumed would have produced a de- 

 finite amount of heat. Now, the muscular heat actually 

 developed during the rotation of the machine fell short 

 of this definite amount, the missing heat being repro- 

 duced to the last fraction in the glowing platinum wire 

 and the other parts of the machine. Here, then, the 

 electric current intervenes between my muscles and the 

 generated heat, exactly as it did a moment ago between 

 the voltaic battery and its generated heat. The electric 

 current is to all intents and purposes a vehicle which 

 transports the heat both of muscle and battery to any 

 distance from the hearth where the fuel is consumed. 

 Not only is the current a messenger, but it is also an 

 intensifier of magical power. The temperature of 

 my arm is, in round numbers, 100 Fahr., and it is 

 by the intensification of this heat that one of the most 

 refractory of metals, which requires a heat of 3,600 

 Fahr. to fuse it, has been reduced to the molten con- 

 dition. 



Zinc, as I have said, is a fuel far too expensive to 

 permit of the electric light produced by its combustion 

 being used for the common purposes of life, and you 

 will readily perceive that the human muscles, or even 

 the muscles of a horse, would be more expensive still. 

 Here, however, we can employ the force of burning coal 



