1821.] Magnetic Phenomena produced by Electricity. 85 



cisely the same laws as in the voltaic circuit ; the needle under 

 the wire, the positive conductor being on the right hand, offering 

 its north pole to the face of the operator, and the needle above, 

 exhibiting the opposite polarity. 



So powerful was the magnetism produced by the discharge of 

 an electrical battery of 17 square feet highly charged, through 

 a silver wire of l-20th of an inch, that it rendered bars of steel 

 of two inches long, and from l-20th to l-10th in thickness, so 

 magnetic, as to enable them to attract small pieces of steel wire 

 or needles ; and the effect was communicated to a distance of 

 five inches above or below or laterally from the wire, through 

 water or thick plates of glass or metal electrically insulated. 



The facility with which experiments were made with the 

 common Leyden battery, enabled me to ascertain several cir- 

 cumstances which were easy to imagine, such as that a tube 

 filled with sulphuric acid of one-fourth of an inch in diameter, 

 did not transmit sufficient electricity to render steel magnetic ; 

 that a needle placed transverse to the explosion through air, was 

 less magnetized than when the electricity was passed through 

 wire ; that steel bars exhibited no polarity (at least at their 

 extremities) when the discharge was made through them as 

 part of the circuit, or when they were placed parallel to the dis- 

 charging wire ; that two bars of steel fastened together, and 

 having the discharging wire placed through their common centre 

 of gravity, showed little or no signs of magnetism after the dis- 

 charge till they were separated, when they exhibited their north 

 and south poles opposite to each other, according to the law of 

 position. 



These experiments distinctly showed, that magnetism was 

 produced whenever concentrated electricity passed through 

 •space; but the precise circumstances, or law of its production, 

 were not obvious from them. When a magnet is made to act 

 on steel filings, these filings arrange themselves in curves round 

 the poles, but diverge in right lines ; and in their adherence to 

 each other form right lines, appearing as spicula. In the attrac- 

 tion of the filings round the wire in the voltaic circuit, on the 

 contrary, they form one coherent mass, which would probably 

 be perfectly cylindrical were it not for the influence of gravity. 

 In first considering the subject, it appeared to me that there 

 must be as many double poles as there could be imagined points 

 of contact round the wire ; but when I found the north and south 

 poles of a needle uniformly attracted by the same quarters of 

 the wire, it appeared to me that there must be four principal 

 poles corresponding to these four quarters. You, however, 

 pointed out to me that there was nothing definite in the poles, 

 and mentioned your idea, that the phenomena might be 

 explained, by supposing a kind of revolution of magnetism round 

 the axis of the wire, depending for its direction upon the posi- 



