ACTION OF MAGNETS ON COPPER AND GOOD CONDUCTORS. 39 
forming 1 , for instance, an angle of 45° with the face, then the induced currents will 
move generally in a plane corresponding more or less to that angle, nearly as they 
do in the examining helix (2333.), if it be inclined in the same manner. This throws 
the polar axis of the bar of copper on one side, so that the north polarity is not directly 
opposed to the north pole of the inducing magnet, and hence the action both of this 
and the other magnetic pole upon the two polarities of the copper will be to send it 
further round, or to place it edgeways to the poles, or with its breadth parallel to the 
magnetic resultant passing through it (2323.) : the bar therefore receives an impulse, 
and the angle of it nearest to the magnet appears to be pulled up towards the magnet. 
This action of course stops the instant the magnetism of the helix core ceases to rise, 
and then the motion due to this cause ceases, and the copper is simply subject to the 
action before described (2295.). At the same time that this twist or small portion 
of a turn round the point of suspension occurs, the centre of gravity of the whole 
mass is repelled, and thus I believe all the actions up to this condition of things is 
accounted for. 
2336. Then comes the revulsion which occurs upon the cessation of the electric 
current, and the falling of the magnetism in the core. According to the law of mag- 
neto-electric induction, the disappearance of the magnetic force will induce brief 
currents in the copper bar (28.), but in the contrary direction to those induced in 
the first instance; and therefore the virtual magnetic pole belonging to the copper 
for the moment, which is nearest the north end of the electro-magnet, will be a south 
pole ; and that which is furthest from the same pole of the magnet will be a north 
pole. Hence will arise an exertion of force on the bar tending to turn it round its 
centre of suspension in the contrary direction to that which occurred before, and 
hence the apparent revulsion ; for the angle nearest the magnetic pole will recede 
from it, the broad face (2323.) or length (2315.) of the bar will come round and face 
towards the magnet, and an action the reverse in every respect of the first action will 
take place, except that whereas the motion was then only a few degrees, now it may 
extend to two or three revolutions. 
2337. The cause of this difference is very obvious. In the first instance, the bar of 
copper was moving under influences powerfully tending to retard and stop it (2329.) ; 
in the second case these influences are gone, and the bar revolves freely with a force 
proportionate to the power exerted by the magnet upon the currents induced by its 
own action. 
2338. Even when the copper is of such form as not to give the oblique resultant 
of magnetic action from the currents induced in it, when, for instance, it is a cube 
or a sphere, still the effect of the action described above is evident (2325.). When a 
plate of copper about three-fourths of an inch in thickness, and weighing two pounds, 
was sustained upon some loose blocks of wood and placed about OT of an inch from 
the face of the magnetic pole, it was repelled and held off a certain distance upon the 
making and continuing of electric contact at the battery ; and when the battery cur- 
