12 
Sir Humphry Davy on the 
parts of one combination, the effect was very much greater - 
This was shown still more distinctly in the following experi- 
ment. 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 quan- 
tity 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 w r as distinctly 
shown in transmitting the electricity of twelve batteries of 
ten plates each of zinc, with double copper arranged as three, 
through fine platinum wire, which when so intensely ignited 
as to be near the point of fusion, exhibited the strongest mag- 
netic 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 w'ould 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 battery was discharged through it. 
