94 JWr. Bennet's Experiments on a new 
needle, Mr. Cavallo repeated the experiment with six yards 
of steel wire twisted in various directions, so as to be admitted 
into the pot ; in which case the metal presented a large surface 
to the acid, and was not subject to be moved by the effer- 
vescence. On adding the diluted vitriolic acid, the needle 
came somewhat more than half a degree nearer to the pot. 
After considering the influence of heat in the above experi- 
ments, and that the motion of the needle was only half a de- 
gree, it may reasonably be suspected to be occasioned by the 
heat of the vessel : yet I think it may also be accounted for by 
the change of magnetism in the twisted wire ; for, after trying 
several times to produce this attraction, by pouring the diluted 
vitriolic acid on a number of bits of wire tied to the end of a 
glass tube without twisting, I could not produce any increased 
attraction ; at last, by twisting the wire, I succeeded to pro- 
duce a degree of attraction, which I thought was owing to the 
expansion or untwisting of the wire during the effervescence. 
This opinion was strengthened by the changes of polarity I 
could so easily produce in softened steel wire ; first by passing 
it through a candle, by which it would acquire a very sensible 
polarity, according to the position in which it was cooled ; 
secondly, by slightly drawing it through my fingers, held in 
different directions in respect to the earth’s polarity ; thirdly, 
when a wire, three inches long, was fastened to the end of a 
glass tube, and deprived of sensible polarity, by passing 
through a candle at right angles to the magnetic meridian, it 
would become possessed of sensible polarity by a small blow 
with my finger on the glass tube, whilst held in a proper po- 
sition ; fourthly, the smallest degree of pressure between my 
fingers, so as to bend the wire, would give it polarity. Now, 
