160 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
coal gas retorts, also produced the current, but ordinary charcoal did not. 
Neither could I obtain any sensible effects with brine, sulphuric acid, saline 
solutions, &c., whether rotated in basins, or inclosed in tubes and passed be¬ 
tween the poles. 
133. I have never been able to produce any sensation upon the tongue by 
the wires connected with the conductors applied to the edges of the revolving- 
plate (88.) or slips of metal (101.). Nor have I been able to heat a fine platina 
wire, or produce a spark, or convulse the limbs of a frog. I have failed also to 
produce any chemical effects by electricity thus evolved (22. 56.). 
134. As the electric current in the revolving copper plate occupies but a 
small space, proceeding by the poles and being discharged right and left at very 
small distances comparatively; and as it exists in a thick mass of metal pos¬ 
sessing almost the highest conducting power of any, and consequently offering 
extraordinary facility for its production and discharge ; and as, notwith¬ 
standing this, considerable currents may be drawn off which can pass through 
narrow wires, forty, fifty, sixty, or even one hundred feet long; it is evident 
that the current existing in the plate itself must be a very powerful one, when 
the rotation is rapid and the magnet strong. This is also abundantly proved 
by the obedience and readiness with which a magnet ten or twelve pounds in 
weight follows the motion of the plate and will strongly twist up the cord by 
which it is suspended. 
135. Two rough trials were made with the intention of constructing mag¬ 
neto-electric machines. In one, a ring one inch and a half broad and twelve 
inches external diameter, cut from a thick copper plate, was mounted so as to 
revolve between the poles of the magnet and represent a plate similar to those 
formerly used (101.), but of interminable length; the inner and outer edges were 
amalgamated, and the conductors applied one to each edge, at the place of the 
magnetic poles. The current of electricity evolved did not appear by the gal¬ 
vanometer to be stronger, if so strong, as that from the circular plate (88.). 
136. In the other, small thick discs of copper or other metal, half an inch 
in diameter, were revolved rapidly near to the poles, but with the axis of rota¬ 
tion out of the polar axis ; the electricity evolved was collected by conductors 
applied as before to the edges (86.). Currents were procured, but of strength 
much inferior to that produced by the circular plate. 
