DOVE ON THE ELECTRICITY OF INDUCTION. 123 



ways exerted in the same manner, and not alternately in opposite 

 directions. The excess of power in the bundle of Avires was so 

 great, that even with seventy wires one line in thickness in one 

 spiral, and the cylinder of soft iron in the other, the steel was 

 magnetized in the direction of the current excited by the bundle 

 of wires, although 110 wires did not neutralize the action of the 

 cylinder in the galvanometer. When the induction-spirals were 

 connected in the same direction, and both contained bundles of 

 wires, I was enabled to invert the polarity of a well-hardened 

 galvanometer needle. It is generally to be observed in experi- 

 menting with such currents, as is the case in galvanometric 

 measurements with frictional electricity, that great changes occur 

 in the length of the oscillations of a previously astatic needle. 



25. A horseshoe of soft iron wound round with wire was now 

 connected with the induction-spirals. The current excited bv a 

 solid cylinder, as well as that caused by a bundle of wires, 

 magnetized it in such a manner, that iron filings strewed upon 

 it stood on end, and a magnetic needle placed near it was power- 

 fully deflected. With opposing currents, the one of which was 

 excited by a cylinder of soft iron, and the other by 100 wires, 

 when the magnetizing spiral with the steel needle and the horse- 

 shoe of soft iron covered with silk were simultaneously placed 

 in the closed circuit of the induced current, the soft iron horse- 

 shoe was magnetized in the direction of the first current, whilst 

 the steel needle was magnetized in an opposite direction, i. e. in 

 the direction caused by the wires. Now, as a continuous cui- 

 rent is required to electro-magnetize soft iron, whilst steel is 

 magnetized by the most sudden discharges, this experiment may 

 be considered pretty conclusive in favour of the assumption 

 which follows from all the other facts, that in the ctcrrent in- 

 duced by a bundle of wires, a certain quantity of electricity is cir- 

 culating in a shorter time than ivhen that quantity is set in mo- 

 tion by a solid cylinder. 



3. Sparks, heating effects, and chemical decomposition. 



26. W^hen the same \\ire is traversed by two currents cir- 

 culating in opposite directions, no spark is produced on dis- 

 connecting the wire when both currents neutralize each other. 

 When therefore a massive cylinder and a bundle of wire oppose 

 each other, and a spark is obtained at the differential inductor, 

 by diminishing or increasing the number of wires the spark may 



