192 MR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 
252. When the marked pole was put at the side of the iron plate at a certain 
distance, the number of vibrations was only five. When the marked pole of 
the second bar was put on the opposite side of the plate at the same distance 
(250.), the vibrations were reduced to two. But when the second pole was an 
unmarked one, yet occupying exactly the same position, the vibrations rose to 
twenty-two. By removing the stronger of these two opposite poles a little way 
from the plate, the vibrations increased to thirty-one, or nearly the original 
number. But on removing it altogether, they fell to between five and six. 
253. Nothing can be more clear, therefore, than that with iron, and bodies 
admitting of ordinary magnetic induction, opposite poles on opposite sides of 
the edge of the plate neutralize each other’s effect, whilst similar poles exalt the 
action ; a single pole end on is also sufficient. But with copper, and substances 
not sensible to ordinary magnetic impressions, similar poles on opposite sides of 
the plate neutralize each other ; opposite poles exalt the action; and a single 
pole at the edge or end on does nothing. 
254. Nothing can more completely show the thorough independence of the 
effects obtained with the metals by Arago, and those due to ordinary magnetic 
forces ; and henceforth, therefore, the application of two poles to various moving 
substances will, if they appear at all magnetically affected, afford a proof of the 
nature of that affection. If opposite poles produce more effect than one, the 
force will be due to electric currents. If similar poles produce more effect 
than one, then the power is not electrical : it will not be like that active in the 
metals and carbon when moving, and in most cases will probably be found to 
be not even magnetical, but the result of irregular causes not anticipated and 
guarded against. 
255. The result of these investigations tends to show that there are really 
but very few bodies that are magnetic in the manner of iron. I have often 
sought for indications of this power in the common metals and other sub- 
stances ; and once in illustration of Arago’s objection (82.), and in hopes of 
ascertaining the existence of currents in metals by the momentary approach of 
a magnet, suspended a disc of copper by a single fibre of silk in an excellent 
vacuum, and approximated powerful magnets on the outside of the jar, making 
them approach and recede in unison with a pendulum that vibrated as the 
disc would do : but no motion could be obtained ; not merely, no indication of 
