xJt) THE ELECTRIC TELEGRAPH. 



quence, the hope of obtaining electricity from ordinary mag- 

 netism, have stimulated me at various times to investigate 

 experimentally the inductive effects of electric currents. I 

 lately arrived at positive results, and not only had my hopes 

 fulfilled, but obtained a theory which appeared to me to open 

 out a full explanation of Arago's magnetic phenomena, and 

 also to discover a new state which may probably have great 

 influence in some of the most important effects of electric 

 currents." 



The first successful experiment of Faraday was made with 

 203 feet of copper wire, coiled in one length on a wooden 

 bobbin, and a similar length interposed on the same bobbin 

 between the turns of the first coil. The wires were insulated 

 from each other by twine. The ends of one of the coils were 

 connected to the two ends of a multiplier with a finely sus- 

 pended magnetic needle a galvanometer ; and the ends of 

 the other coil with a battery of one hundred pairs of four- 

 inch square plates with double coppers. When contact was 

 made with the battery, there was, says Faraday, a sudden 

 and very slight effect at the galvanometer, and there was 

 also a similar slight effect when the contact with the battery 

 was broken. But during the continuance of the voltaic 

 current through the one helix, no galvanometer appear- 

 ances, nor any effect like induction upon the other helix, 

 could be perceived. 



Faraday began these experiments in 1831 and continued 

 them during following years. He found that not only 

 were currents induced in helices by induction of others in 

 their neighbourhood in which currents were passing, but 

 that on inserting the end of a permanent magnet into the 

 middle of a helix of wire, a current of electricity was gene- 

 rated whose direction depended upon the pole inserted and 

 the end of the spiral with regard to the direction of its 

 windings. He says, " If such a hollow helix as that described 

 be laid east and west, or in any other constant position, and 

 a magnet be retained east and west, its marked pole always 

 being one way, then, whichever end of the helix the magnet 

 goes in at, and, consequently, whichever pole of the magnet 

 enters first, still the needle is deflected the same way : on 



