26 



ing the north pole of a magnet near a piece of soft iron, the nearer 

 end of the iron is of south polarity, and the farther of north. This 

 is called induced magnetism, because the magnetism of the piece 

 of soft iron is induced by the near presence of the permanent 

 magnet. 



We can also have induced currents of electricity. If a wire 

 through which an electric current is flowing be brought near a 

 second wire, through the latter will also run a current, but in the 

 opposite direction to the first, and only momentary. So long as 

 the two wires are kept together, no further induced current will 

 flow. But on withdrawing the wire connected with the battery, 

 another induced current will flow through the other wire, again 

 momentary, but this time in the opposite direction to the former 

 one, and therefore in the same direction as the current from the 

 battery. 



I will illustrate this by connecting tnis bobbin of wire with this 

 delicate galvanometer, which consists simply of a small magnet 

 placed in the centre of a coil of wire. So sensitive is the magnetic 

 needle in the galvanometer, that if a feeble current of Electricity 

 be started round the coil, it will be defected. 



I connect another coil of wire with the battery, so that a strong 

 electric current is sent through it ; this one I shall rapidly insert 

 in the bobbin, and the defection of the needle informs us that a 

 current of Electricity has been induced in the wire round the 

 bobbin ; but only for a moment ; the needle quickly resumes its 

 Original position, shewing that no more Electricity is flowing round 

 it. 



Directly however I withdraw the coil, the defection of the needle 

 again informs us that another induced current is started, but this 

 time in the opposite direction to the first, as the needle moves in 

 the opposite direction. So we can have induced currents of Elec- 

 tricity as well as induced magnetism. Perhaps this can be shown 

 plainer by using the lantern galvanometer so that the movements 

 of the needle can be thrown upon the screen. 



If, instead of a coil of wire being inserted in the bobbin, a 

 permanent magnet be used, we have the same results. 



An electro-magnet may likewise be used. Over this powerful 

 one which is connected with the galvanometer, I will rapidly bring 

 down another electro-magnet, this one being connected with the 

 battery, and we have the same approach causing deflection in one 

 direction, and withdrawal in the opposite, and the currents only 

 momentary. 



What I particularly wish to draw your attention to is, that these 

 induced currents are only momentary, and that the quicker the 

 a^proach^.or the withdrawal, the greater the deflection, proving 



