Electricity. 333 



constructed by Gordon completes the circuit fi,000 times in a second 

 and breaks it as often. The advantage of the induction apparatus is 

 that the current of a voltaic battery which has large heating and chem- 

 ical power with low potential, is exchanged for an electrical current of 

 low chemical and heating power, but very high potential. So that while 

 it is possible to get only a short spark from a voltaic circuit, the same 

 current is able to induce a secondary current which will give a spark 

 several hundred times as long. Induction machines have been made to 

 deliver a spark over three feet long. The case of the induction current 

 is no exception to the rule that energy is required to produce energy. 

 Because when the coil from the battery is moved toward the conduction 

 coil, or left hand coil, the current induced in the latter is contrary, and 

 contrary currents repel bodily, so that as soon as the current is produced 

 the repulsion commences. In other words, the molar motion of the 

 coils, or coil, is converted into a repellent current, and the molar motion 

 is resisted and at the same time heat is developed in the conducting coil. If 

 a metallic top be set to spinning near two iron* poles which can suddenly 

 be converted "into the poles of a powerful electro-magnet," when the 

 poles become magnetic by a current through them the top is soon 

 brought to rest. The reason is that the magnetic currents in the mag- 

 net produce in the top which is a conductor alternately, on its revolv- 

 ing surface approaching and receding from the magnet, a series of sec- 

 ondary induced currents, which by their repellent power tend to turn the 

 top backwards, and this effort results in converting the energy of the 

 currents into heat, the same as if the top were stopped by friction. But 

 it is observed that if the top in this case were compelled by force to 

 turn continuously in the presence of this current, and wires contrived 

 to conduct away the electricity induced in it, we should have a con- 

 tinuous ( alternating ) current from the top. In fact, we should have 

 an electric dynamo to all intents and purposes. 



A d} r namo usually consists essentially of series of bobbins or coils of 

 wire fastened upon the periphery of a wheel, which is made to revolve 

 between the poles of powerful magnets. In the earlier machines the 

 magnets used were strong, permanent, steel magnets. In the later 

 ones, the magnets are electro-magnets. These electro-magnets were at 

 first charged by small side dynamos, which revolved in the presence of 

 permanent steel magnets, and the great currents used for lighting, &c. , 

 were generated by the bobbins revolving between the great electro-mag- 

 nets so charged. But after awhile it was discovered that after the great 

 electro-magnets were once charged the charge did not entirety leave 

 them when the current around them was discontinued. So that when 

 the bobbins were revolved in their presence a slight current was cre- 

 ated through the bobbins. It was then suggested to run this current 



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