350 Mr. Faraday on the Magneto-electric Spark and Shock, 



have used the natural magnet, but in all cases the secondary 

 magnet was a piece of soft iron. 



The spark is never the electricity of the principal, or even 

 of the secondary magnet. The power in the first induces a 

 corresponding power in the second, and that induces a motion 

 of the electricity in the wire round the latter, which electricity 

 produces the spark. It seemed to me, however, no difficult 

 matter to dispense with the secondary or temporary magnet, 

 and thus approach a step nearer to the original one; and this 

 was easily accomplished in the following manner. About 20 

 feet of silked copper wire were made into a short ring helix, 

 on one end of a pasteboard tube, through which a cylindrical 

 magnet, an inch in diameter, could move freely; one end of the 

 helix wire was fastened to a small amalgamated copper plate, 

 and the other end bent round so as to touch this plate perpen- 

 dicularly upon its flat surface, and also in such a manner that 

 when the magnet was passed through the cylinder it should 

 come against this wire, and separate the end from contact 

 with the plate. The consequence was that whenever this ac- 

 tion was quickly performed, the magneto-electric spark ap- 

 peared at the place of disjunction. 



My apparatus was placed horizontally, and a short loos 

 plug of wood was put into the 

 end of the cylinder, so that the 

 disjunction at the plate should 

 take place at the moment the 



end of the magnet was passing (Q_Jj|| — ) -> 



through the helix ring, that be- 

 ing the most favourable condi- 

 tion of the apparatus. The mag- 

 net was driven with a sharp quick motion through the cylin- 

 der, its impetus being overcome, as soon as the spark was ob- 

 tained, by an obstacle placed at a proper distance on the out- 

 side of the moveable wire. From the brightness and appear- 

 ance of the spark, I have no doubt that if both ends of a 

 horse-shoe magnet were employed, and a jogging motion were 

 communicated to the light frame carrying the helices, a spark 

 equal, if not superior, to those which down to this time have 

 been obtained with magnets of a certain power, would be pro- 

 duced. 



Thus the magneto-electric spark has been brought one step 

 nearer to the exciting magnet. The much more important 

 matter still remains to be effected of rendering that electricity 

 which is in the magnet itself, and gives it power, evident under 

 the form of the spark. 



The next point to which I wish to direct your attention is 



