132 DOVK ON THE ELECTRICITY OF INDUCTION. 



tery has the same properties therefore as that produced by the 

 connecting wire of a galvanic battery. 



III. Currents mduced by the evanescent magnetism of electro- 

 magnetized rods of iron and bundles of wires, when the 

 current magnetizing them is produced — 



1. By the approach of an entire copper wire to a steel 



magnet. 



2. By the approach of soft iron to a steel magnet. 



3. By the combination of both methods of excitation 



in Saxton's machine. 



39. Whilst a magnet at rest only exerts an influence upon what 

 are called magnetic metals, exciting in them magnetic polarity by 

 communication, the action of a magnet in motion is known to 

 affect all the metals, producing in them electrical cuiTcnts. In- 

 stead of moving a magnet mechanically, magnetism can also be 

 produced and destroyed in a stationary bar of iron by the ap- 

 proach and removal of a steel magnet. If a powerful action is 

 required, the wire in which the electric current is to be produced 

 must surround with numerous coils the bar of iron which is to 

 be magnetized. If the magnetizing is effected by the approach 

 of a magnet to the iron rod, a mixed result is obtained produced 

 by two excitations ; for when the magnet approaches the iron, 

 it approaches at the same time the coil of wire which surrounds 

 it. The effect of this approach must on no account be over- 

 looked, for I have obtained with a machine constructed on the 

 principle of Saxton's machine, the cylindrical coils of which 

 however contained no iron, such powerful shocks, when the hands 

 were wetted and the keeper quickly rotated, that it was diffi- 

 cult, on account of the resulting cramp, to open my hands. 

 But there is a means of neutralizing the effect produced by the 

 approximation of the wire to the magnet. As a current in an 

 opposite direction is produced in a spiral brought near the 

 north pole of a magnet, to that which is produced in a similar 

 spiral brought near to the south pole, it is only necessary to 

 coil the wii'e surrounding the iron rod into another similar 

 spiral, and to approximate this empty spiral in the same manner 

 to the south pole as the one containing the iron nucleus is ap- 

 proximated to the north pole. The currents produced in the wire 



