THE ELECTRIC LIGHT. 060 
an 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. Daring 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 Faraday's discovery, which opens out 
to us the prospect of being able to apply the electric light 
to public use. 
