158 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
former would be the force excited in making’ the plate revolve with the mag- 
net, or the magnet with the plate ; the latter would be a repulsive force, and is 
probably that, the effects of which M. Arago has discovered (82.). 
126. The extraordinary circumstance accompanying this action, which has 
seemed so inexplicable, namely, the cessation of all phenomena when the mag- 
net and metal are brought to rest, now receives a full explanation (82.) ; for 
then the electrical currents which cause the motion, cease altogether. 
12/. All the effects of solution of metallic continuity, and the consequent 
diminution of power described by Messrs. Babbage and Herschel # , now re- 
ceive their natural explanation, as well also as the resumption of power when 
the cuts were filled up by metallic substances, which, though conductors of 
electricity, were themselves very deficient in the power of influencing magnets. 
And new modes of cutting the plate may be devised, which shall almost en- 
tirely destroy its power. Thus, if a copper plate (81.) be cut through at about 
a fifth or sixth of its diameter from the edge, so as to separate a ring from it, 
and this ring be again fastened on, but with a thickness of paper intervening 
(fig. 29.), and if Arago’s experiment be made with this compound plate so ad- 
justed that the section shall continually traverse opposite the pole, it is evident 
that the magnetic currents will be greatly interfered with, and the plate probably 
lose much of its effectq~- 
An elementary result of this kind was obtained by using two pieces of 
thick copper, shaped as in fig. 28. When the two neighbouring edges were 
amalgamated and put together, and the arrangement passed between the 
poles of the magnet, in a direction parallel to these edges, a current was urged 
through the wires attached to the outer angles, and the galvanometer became 
strongly affected ; but when a single film of paper was interposed, and the 
experiment repeated, no sensible effect could be produced. 
128. A section of this kind could not interfere much with the induction of 
magnetism, supposed to be of the nature ordinarily received by iron. 
129. The effect of rotation or deflection of the needle, which M. Arago ob- 
tained by ordinary magnets, M. Ampere succeeded in procuring by electro- 
* Philosophical Transactions, 1825, p. 481. 
t This experiment has actually been made by Mr. Christie, with the results here described, and 
is recorded in the Philosophical Transactions for 1827. p. 82. 
