Experimental Researches in Electricity. 



helix, was, to all intents and purposes, a magnet ; and hence 

 the step from volta-electric to magneto-electric induction 

 was an immediate and necessary one. As introductory how- 

 ever to the use of the magnet itself, Faraday experi- 

 mented on the effects of adding an iron core to his helices ; 

 and when this was done, it was found that, using the same 

 strength of battery, the influence of the current, as indicated 

 by the galvanometer, was tenfold greater than when no 

 iron was present. So powerful indeed was the impetus 

 communicated to the galvanometer needle, that when the 

 battery of one hundred pairs of plates was used, it spun 

 round three or four times before the action of the air, 

 and terrestrial magnetism could reduce its motion to 

 simple oscillation : a minute spark was also exhibited by 

 using charcoal terminations to the inducible wire, invaria- 

 bly on making, but rarely on breaking contact at the bat- 

 tery. 



A pair of common bar magnets was then substituted for 

 the galvanic battery, and it was then found that by simply 

 making, and breaking magnetic contact, powerful electrical 

 currents were induced in the helices employed. The de- 

 tails of the first experiment by which this discovery was estab- 

 lished are so short and simple, that we shall transcribe them 

 here. " A combination of helices, like those above described, 

 was constructed upon a hollow cylinder of pasteboard ; there 

 were eight lengths of copper wire, containing altogether 

 220 feet : all of these helices were connected end to end, and 

 then with the galvanometer, by means of two copper wires, 

 each five feet in length. A soft iron cylinder, seven-eighths 

 of an inch thick, and twelve inches long, was introduced into 

 the pasteboard tube ; a couple of bar magnets were arranged 

 with their opposite poles at one end in contact, so as to resem- 

 ble a horse-shoe magnet, and then contact made between the 

 other poles, and the ends of the iron cylinder, so as to 

 convert it for a time into a magnet. Upon making mag- 



