THE ELECTRIC LIGHT. 559 



round it, and obtained thereby greatly augmented effects between suit- 

 ably placed magnetic poles. Such an armature is employed in the 

 small magneto-electric machine which I now introduce to your notice, 

 and for which the institution is indebted to Mr. Henry Wilde, of Man- 

 chester. There are here sixteen permanent horseshoe magnets placed 

 parallel to each other, and between their poles a Siemens armature. 

 The two ends of the wire which surrounds the armature are now dis- 

 connected. In turning the handle and causing the armature to rotate, 

 I simply overcome ordinary mechanical friction. But the two ends of 

 the armature coil can be united in a moment, and when this is done I 

 immediately experience a greatly increased resistance to rotation. 

 Something over and above the ordinary friction of the machine is now 

 to be overcome, and by the expenditure of an additional amount of 

 muscular force I am able to overcome 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 connect- 

 ing 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 armature is broken, an in- 

 stant 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 ex- 

 ternal work the matter consumed would have produced a definite amount 

 of heat. Now, the muscular heat actually developed during the rota- 

 tion 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° 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 to turn our machine, 

 and it is this employment of our cheapest fuel, rendered possible by 



