190 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
or no magnetic curves are intersected (114.); and therefore the magnet should 
remain at rest. On the contrary, if the action of a north magnetic pole were 
to produce a southness in the nearest part of the copper plate, and a diffuse 
northness elsewhere (82.), as is really the case with iron; then the use of another 
north pole on the opposite side of the same part of the plate should double 
the effect instead of destroying it, and double the tendency of the first magnet 
to move with the plate. 
245. A thick copper plate (85.) was therefore fixed on a vertical axis, a bar 
magnet was suspended by a platted silk cord, so that its marked pole hung 
over the edge of the plate, and a sheet of paper being interposed, the plate was 
revolved; immediately the magnetic pole obeyed its motion and passed off in 
the same direction. A second magnet of equal size and strength was then sus¬ 
pended to the first, so that its marked pole should hang beneath the edge of 
the copper plate in a corresponding position to that above, and at an equal 
distance (fig. 3/.). Then a paper sheath or screen being interposed as before, 
and the plate revolved, the poles were found entirely indifferent to its motion, 
although either of them alone would have followed the course of rotation. 
246. On turning one magnet round, so that opposite poles were on each 
side of the plate, then the mutual action of the poles and the moving metal was 
a maximum. 
24f. On suspending one magnet so that its axis was level with the plate, 
and either pole opposite its edge, the revolution of the plate caused no motion 
of the magnet. The electrical currents dependent upon induction would now 
tend to be produced in a vertical direction across the thickness of the plate, 
but could not be so discharged, at least only to so slight a degree as to leave all 
effects insensible ; but ordinary magnetic induction, or that on an iron plate, 
would be equally if not more powerfully developed in such a position (251.). 
248. Then, with regard to the production of electricity in these cases:—when¬ 
ever motion was communicated by the plate to the magnets, currents existed; 
when it was not communicated, they ceased. A marked pole of a large bar 
magnet was put under the edge of the plate; collectors (86.) applied at the axis 
and edge of the plate as on former occasions (fig. 38.), and these connected 
with the galvanometer; when the plate was revolved, abundance of electricity 
passed to the instrument. The unmarked pole of a similar magnet was then 
