ON FARADAY'S LINES OF FOKCE. 185 



The number of unit lines* of magnetic force due to a closed current depends 

 on the form as well as the quantity of the current, but the number of unit 

 cells')- in each complete line of force is measured simply by the number of unit 

 currents which embrace it. The unit cells in this case are portions of space in 

 which unit of magnetic quantity is produced by unity of magnetizing force. 

 The length of a cell is therefore inversely as the intensity of the magnetizing 

 force, and its section inversely as the quantity of magnetic induction at that 

 point. 



The whole number of cells due to a given current is therefore proportional 

 to the strength of the current multiplied by the number of lines of force 

 which pass through it. If by any change of the form of the conductors the 

 number of cells can be increased, there will be a force tending to produce that 

 change, so that there is always a force urging a conductor transverse to the 

 lines of magnetic force, so as to cause more lines of force ^o pass through the 

 closed circuit of which the conductor forms a part. 



The number of cells due to two given currents is got by multiplying 

 the number of lines of inductive magnetic action which pass through each by 

 the quantity of the currents respectively. Now by (9) the number of lines 

 which pass through the first current is the sum of its own lines and those 

 of the second current which would pass through the first if the second current 

 alone were in action. Hence the whole number of cells will be increased by 

 any motion which causes more lines of force to pass through either circuit, 

 and therefore the resultant force will tend to produce such a motion, and the 

 work done by this force during the motion will be measured by the number 

 of new cells produced. All the actions of closed conductors on each other may 

 be deduced from this principle. 



On Electric Currents produced by Induction. 



Faraday has shewnj that when a conductor moves transversely to the lines 

 of magnetic force, an electro-motive force arises in the conductor, tending to 

 produce a current in it. If the conductor is closed, there is a continuous 

 current, if open, tension is the result. If a closed conductor move transversely 

 to the lines of magnetic induction, then, if the number of lines which pass 



* Exp. Res. (3122). See Art. (6) of this paper. t Art. (13). 



J Exp. Res. (3077), &c. 

 VOL. I. 24 



