new phenomenon of electro-magnetism . 157 
brought near each other on surfaces of mercury, that repul- 
sion takes place. 
Nor can the effect be referred to that kind of action which 
occurs when electricity passes from good into bad conduc- 
tors, as in the phenomena of points electrified in air, as the 
following facts seem to prove. Steel wires were substituted 
for copper wires, and the appearances were the same in 
kind, and only less in degree ; without doubt, in consequence 
of a smaller quantity of electricity passing through the steel 
wires : and by comparing the conducting powers of equal 
cylinders of mercury and steel in glass tubes, by ascertaining 
the quantity of iron filings they attracted, it was found that 
the conducting powers of mercury were higher than those of 
steel ; the first metal taking up fifty-eight grains of iron 
filings, and the second only thirty-seven. 
Again ; fused tin was substituted for mercury in a porcelain 
vessel into which wires of copper and steel were alternately 
ground and fixed : the elevations were produced as in the 
mercury, and the phenomena of rotation by the magnet ; and 
it was found by direct experiment, that the conducting powers 
of the tin, at and just before its point of fusion, did not percep- 
tibly differ, and that they were much higher than those of mer- 
cury. Lastly, the communication was made from the battery 
by two tubes having nearly the same diameter as the wires, 
filled with mercury, so that the electricity, for some inches 
before it entered the basin, passed through mercury ; and 
still the appearances continued the same. 
From the rapidity of the undulations round the points of 
the cones, I thought they would put in motion any light 
bodies placed above the mercury ; but I could not produce 
