284 Prof. Norton on Molecular Physics. 



of the magnet, or a recess of the wire from the current, or a 

 movement of the wire in the magnetic field attended with a di- 

 minished action of the entire impulsive force of the magnet. 



The oppositely directed currents induced by alternately closing 

 and breaking the galvanic circuit, when the two contiguous 

 wires are formed into a hollow coil, are greatly augmented by 

 inserting rods or bundles of iron wire within the coil. The 

 explanation of this is, doubtless, that the direct action of the 

 galvanic current is reinforced by the magnetic currents which it 

 developes in the iron. The other cases of induction above referred 

 to need not be dwelt upon, with the exception of that resulting 

 from the movement of a wire to different points of the magnetic 

 field. 



This case has been subjected to a rigorous experimental ana- 

 lysis by Faraday, who has deduced from his researches the follow- 

 ing general results. If a wire, forming part of a closed circuit, 

 be held in a direction transverse to a magnet, and moved in the 

 magnetic field, across the " lines of force/' or magnetic curves, a 

 current will be induced in the wire. If the wire be moved in 

 one direction across these lines of force, a current in a certain 

 direction will arise, and if it be moved across them in the other 

 direction, a current in the opposite direction will be induced. 

 The quantity of electricity set in motion will depend upon the 

 number of lines of force crossed by the moving wire, and not 

 upon the obliquity of the direction of the motion to these lines. 

 Thus if the wire be placed over the middle of the magnet (in, 

 fig. 9) and moved in any 

 direction from this position 

 across the lines of force as 

 shown in the figure, a cur- 

 rent will be induced in it, 

 running in the same direc- 

 tion as the circular currents 

 on the upper side of the 

 magnet ; and if the wire be 

 moved across these lines to- 

 ward the middle of the m ag- I 

 net, a current will traverse f I 

 the wire in the opposite di- 

 rection. In each case the 



comparative quantity of electricity set in motion will depend 

 solely upon the comparative number of magnetic curves crossed, 

 and not upon the line mr, ms, or mt, along which the movement 

 takes place. 



These facts are in entire accordance with the fundamental prin- 

 ciple of induction stated on page 283. For (1) the impulsive 



Fiff. 9. 



