426 Sir Humphry Davy on the magnetic phenomena 
a small quantity of electricity ; and in both cases they were 
neither attractive of each other, nor of iron filings, and not 
affected by the magnet ; and the only proof of their being 
magnetic, was their occasioning a certain small deviation of 
the magnetized needle. 
Thus, a large piece of charcoal placed in the circuit of a 
very powerful battery, being a very bad conductor compared 
with the metals, would not affect the compass needle at all, 
unless it had a very large contact with the metallic part of the 
circuit; and if a small wire was made to touch it in the 
circuit only in a few points, that wire did not gain the power 
of attracting iron filings ; though, when it was made to touch 
a surface of platinum foil coiled round the end of the charcoal, 
a slight effect of this kind was produced. And in a similar 
manner fused hydrate of potassa, one of the best of the im- 
perfect conductors, could never be made to exert any attrac- 
tive force on iron filings, nor could the smallest filaments of 
cotton moistened by solution of hydrate of potassa, placed in 
the circuit, be made to move by the magnet ; nor did steel 
needles floating on cork on an electrized solution of this kind, 
placed in the voltaic circuit, gain any polarity ; and the only 
proof of the magnetic powers of electricity passing through 
such a fluid, was afforded by its effect upon the magnetized 
needle, when the metallic surfaces, plunged in the fluid, were 
of considerable extent. That the mobility of the parts of 
fluids did not interfere with their magnetic powers as de- 
veloped by electricity, I proved, by electrifying mercury, and 
Newton’s metal fused, in small tubes. These tubes, placed 
in a proper voltaic circuit, attracted iron filings, and gave 
magnetic powers to needles ; nor did any agitation of the 
