THE ELECTRIG LIGHT. 669 



jin additional amount of muscular force I am able to over- 

 come it. The excess of labor thus thrown upon my arm 

 has its exact equivalent in the electric currents generated, 

 and the heat produced by their subsidence in the coil of 

 the armature. A portion of this heat may be rendered 

 visible by connecting the two ends of the coil with a thin 

 platinum 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 arma- 

 ture is broken, an instant relief from the labor thrown 

 upon the arm being the consequence. Clearly realize the 

 equivalent of the heat here developed. During the period 

 of turning the machine a certain amount of combustible 

 substance was oxidized or burned in the muscles of my arm. 

 Had it done no external work, the matter consumed would 

 have produced a definite 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 reproduced 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 degrees 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 

 degrees Fahr. to fuse it, has been reduced to the molten 

 condition. 



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 per- 

 ceive 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 to turn our 

 machine, and it is this employment of our cheapest fuel, 

 rendered possible by Farad ay 's discovery, which opens out 

 to us the prospect of being able to apply the electric light 

 to public use. 



