SECT. XXXII. MAGNETO-ELECTRIC INDUCTION. 323 



broken, but neither chemical action nor any other electric effects 

 were obtained. A deviation of the needle of the galvanometer 

 took place when common magnets were employed instead of the 

 Voltaic current ; so that the magnetic and electric forces are 

 identical in their effects in this experiment. Again, when a 

 helix formed of 220 feet of copper wire, into which a cylinder of 

 soft iron was introduced, was placed between the north and south 

 poles of two bar magnets, and connected with the galvanometer 

 by means of wires from each extremity, as often as the magnets 

 were brought into contact with the iron cylinder it became mag- 

 netic by induction, and produced a deflection in the needle of the 

 galvanometer. On continuing the contact the needle resumed 

 its natural position, and, when the contact was broken, deflection 

 took place in the opposite direction ; when the magnetic contacts 

 were reversed, the deflection was reversed also. With strong 

 magnets, so powerful was the action, that the needle of the gal- 

 vanometer whirled round several times successively ; and similar 

 effects were produced by the mere approximation or removal of 

 the helix to the poles of the magnets. Thus it was proved that 

 magnets produce the very same effects on the galvanometer that 

 electricity does. Though at that time no chemical decomposi- 

 tion was effected by these momentary currents which emanate 

 from the magnets, they agitated the limbs of a frog ; and Dr. 

 Faraday justly observes, that " an agent which is conducted 

 along metallic wires in the manner described, which, whilst so 

 passing, possesses the peculiar magnetic actions and force of a 

 current of electricity, which can agitate and convulse the limbs 

 of a frog, and which finally can produce a spark by its discharge 

 through charcoal, can only be electricity." Soon after he com- 

 pletely established the identity of the two powers by producing 

 the spark, heating metallic wires, and accomplishing chemical 

 decomposition. Hence it appears that electrical currents are 

 evolved by magnets, which produce the same phenomena with 

 the electrical currents from the Voltaic battery : they, however, 

 differ materially in this respect that time is required for the 

 exercise of the magnetico-electric induction, whereas Volta-elec- 

 tric induction is instantaneous. 



Thus the effect of induction or the influence of the spiral wire 

 in increasing the electric and magnetic power is 'very great 

 indeed, and to that we are indebted for the electric telegraph, for 



