LESSONS IN PHTSICS. 97 



the current was temporary. Draw out the primary coil and again 

 the current is shown, but in the opposite direction, and again it 

 appears to be temporary. Again place the primary coil inside 

 the secondary, then break and close the circuit and in each case 

 we have a current in the secondary coil as before. When intro- 

 ducing the primary coil, and when closing the primary circuit, an 

 inverse induction current is formed in the secondary coil, while 

 on withdrawing the primary coil or breaking the primary circuit 

 a direct current is formed in the secondary coil. 



Further, it has been discovered that the same results are 

 reached by using a magnet with the secondary coil, as are 

 reached by using a primary coil. That is, if a magnet be lowered 

 into the secondary coil, an inverse current is indicated in the 

 coil, and if the magnet is removed, a direct current is indicated. 

 Now, if a bar of soft iron be placed in the secondary coil, and the 

 pole of a permanent magnet be brought near it, the soft iron 

 becomes a magnet by induction and a current is manifested in 

 the secondary coil. Now, remove the permanent magnet and the 

 soft iron ceases to be a magnet, and a current is again indicated, 

 but in the opposite direction. 



Again, a permanent magnet is placed within the secondary coil 

 and a bar of soft iron is moved toward it; the magnet causes the 

 soft iron to become a magnet by induction, and this seems to 

 increase or change the magnetism of the permanent magnet, and 

 a current is indicated in the secondary coil, and a current in the 

 opposite direction is shown on the removal of the soft iron. 



The same effect maybe obtained if an electro-magnet be placed 

 within the secondary coil and a strong magnet rotate rapidly 

 in front of it, so that its pole acts inductively upon the branches 

 of electro-magnet in succession. 



Similar results may be obtained by passing coiled wire around 

 the poles of a permanent horseshoe magnet, and revolving the 

 plate of soft iron in front of the poles of the magnet. The soft 

 iron becoming magnetized acts on the permanent magnet, and 

 alternate currents are induced in the coils of the wire. 



On the principles just mentioned many different kinds of ma- 



L. S. 7 



