EXPLICATION OF ARAGO’S MAGNETIC PHENOMENA. 
153 
plates then passed between the magnetic poles, in a direction transverse to 
their length, the same effects were produced (fig. 22.). The parts of the plates 
towards the end may be considered either as mere conductors, or as portions 
of metal in which the electrical current is excited, according to their distance 
and the strength of the magnet ; but the results were in perfect harmony with 
those before obtained. The effect was as strong as when the conductors were 
held against the sides of the plate (101.). 
109. When the mere wire from the galvanometer, connected so as to form 
a complete circuit, was passed through between the poles, the galvanometer 
was affected; and upon passing it to and fro, so as to make the alternate im- 
pulses produced correspond with the vibrations of the needle, they could be 
increased to 20° or 30° on each side the magnetic meridian. 
110. Upon connecting the ends of a plate of metal with the galvanometer 
wires, and then carrying it between the poles from end to end, (as in fig. 23.) 
in either direction, no effect whatever was produced upon the galvanometer. 
But the moment the motion became transverse, the needle was deflected. 
111. These effects were also obtained from electro-magnetic poles, resulting 
from the use of copper helices or spirals, either alone or with iron cores (34. 54.). 
The directions of the motions were precisely the same ; but the action was 
much greater when the iron cores were used, than without. 
112. When a flat spiral was passed through edgeways between the poles, a 
curious action at the galvanometer resulted; the needle first went strongly one 
way, but then suddenly stopped, as if it struck against some solid obstacle, 
and immediately returned. If the spiral were passed through from above 
downwards, or from below upwards, still the motion of the needle was in the 
same direction, then suddenly stopped, and then was reversed. But on turn- 
ing the spiral half-way round, i. e. edge for edge, then the directions of the 
motions were reversed, but still were suddenly interrupted and inverted as 
before. This double action depends upon the halves of the spiral (divided by a 
line passing through its centre perpendicular to the direction of its motion) 
acting in opposite directions ; and the reason why the needle went to the same 
side, whether the spiral passed by the poles in the one or the other direction, 
depended upon the circumstance, that upon changing the motion, the direction 
of the wires in the approaching half of the spiral was changed also. The 
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