1821.] Magnetic Phenomena produced by Electricity. 83* 



circuit of a battery of 30 pairs of plates, of nine inches by five, 

 and tried their magnetism by means of iron filings : they were 

 all magnetic : those which were parallel to the wire attracted 

 filings in the same way as the wire itself, but those in transverse 

 directions exhibited each two poles, which, being examined by 

 the test of delicate magnets, it was found that all the needles 

 that were placed under the wire (the positive end of the battery 

 being east) had their north poles on the south side of the wire, 

 and their south poles on the north side ; and that those placed 

 over had their south poles turned to the south, and their north 

 poles turned to the north ; and this was the case whatever was 

 the inclination of the needles to the horizon. On breaking the 

 connexion, all the steel needles that were on the wire in a trans- 

 verse direction retained their magnetism, which was as powerful 

 as ever, while those which were parallel to the silver wire 

 appeared to lose it at the same time as the wire itself. 



1 attached small longitudinal portions of wires of platinum, 

 silver, tin, iron, and steel, in transverse directions, to a wire of 

 platinum that was placed in the circuit of the same battery. The 

 steel and the iron wire immediately acquired poles in the same 

 manner as in the last experiment ; the other wires seemed to 

 have no effect, except in acting merely as parts of the electrical 

 circuit ; the steel retained its magnetism as powerfully after the 

 circuit was broken as before ; the iron wire immediately lost a 

 part of its polarity, and in a very short time the whole of it. 



The battery was placed in different directions as to the poles 

 of the earth ; but the effect was uniformly the same. All needles 

 placed transversely under the communicating wires, the positive 

 end being on the right hand, had their north poles turned 

 towards the face of the operator, and those above the wire their 

 south poles ; and on turning the wire round to the other side of 

 the battery, it being in a longitudinal direction, and marking the 

 side of the wire, the same side was always found to possess the 

 same magnetism ; so that in all arrangements of needles trans- 

 versely round the wire, all the needles above had north and 

 south poles opposite to those below, and those arranged verti- 

 cally on one side, opposite to those arranged vertically on the 

 other side. 



I found that contact of the steel needles was not necessary, 

 and that the effect was produced instantaneously by the mere 

 juxta-position of the needle in a transverse direction, and that 

 through very thick plates of glass : and a needle that had been, 

 placed in a transverse direction to the wire merely for an instant, 

 was found as powerful a magnet as one that had been long in 

 communication with it. 



I placed some silver wire of l-20th of an inch and some of 

 l-50th in different parts of the voltaic circuit when it was com- 

 pleted, and shook some steel filings on a glass plate above them i 



g 2 



