84 Sir Humphry Davy on [Aug. 



the steel filings arranged themselves in right lines always at 

 right angles to the axis of the wire ; the effect was observed, 

 though feebly, at the distance of a quarter of an inch above the 

 thin wire, and the arrangement in lines was nearly to the same 

 length on each side of the wire. 



I ascertained by several experiments, that the effect was pro- 

 portional to the quantity of electricity passing through a given 

 space, without any relation to the metal transmitting it : thus, 

 the finer the wires the stronger their magnetism. 



A zinc plate of a foot long, and six inches wide, arranged 

 with a copper plate on each side, was connected by a very fine 

 ■wire of platinum, according to your method ; and the plates were 

 plunged an inch deep in diluted nitric acid. The wire did not 

 sensibly attract fine steel filings. When they were plunged two 

 inches, the effect was sensible ; and it increased with the quan- 

 tity of immersion. Two arrangements of this kind acted more 

 powerfully than one ; but when the two were combined so as to 

 make the zinc and copper-plates but parts of one combination, 

 the effect was very much greater. This was shown still more 

 distinctly in the following experiment : Sixty zinc plates with 

 double copper-plates were arranged in alternate order, and the 

 quantity of iron filings which a wire of a determinate thickness 

 took up observed : the wire remaining the same, they were 

 arranged so as to make a series of thirty ; the magnetic effect 

 appeared more than twice as great ; that is, the wire raised more 

 than double the quantity of iron filings. 



The magnetism produced by voltaic electricity seems (the 

 wire transmitting it remaining the same) exactly in the same 

 ratio as the heat ; and however great the heat of a wire, its 

 magnetic powers were not impaired. This was distinctly shown 

 in transmitting the electricity of 12 batteries of 10 plates each 

 of zinc, with double copper arranged as three, through fine pla- 

 tinum wire, which, when so intensely ignited as to be near the 

 point of fusion, exhibited the strongest magnetic effects, and 

 attracted large quantities of iron filings and even small steel 

 needles from a considerable distance. 



As the discharge of a considerable quantity of electricity 

 through a wire seemed necessary to produce magnetism, it 

 appeared probable, that a wire electrified by the common 

 machine would not occasion a sensible effect ; and this I found 

 was the case, on placing very small needles across a fine wire 

 connected with a prime conductor of a powerful machine and 

 the earth. But as a momentary exposure in a powerful electrical 

 circuit was sufficient to give permanent polarity to steel, it 

 appeared equally obvious, that needles placed transversely to a 

 wire at the time that the electricity of a common Leyden bat- 

 tery was discharged through it, ought to become magnetic ; 

 and this I found was actually the case, and according to pre- 



