CHAPTER III. 



RESISTANCE OHM'S LAW MODES OF JOINING CELLS. 



Resistance. In its course a current meets with 

 obstacles to its flow.* This arises from the fact that 

 no bodies are perfect conductors ; the greater the 

 conductivity the less the resistance, as it is called. 

 Metals are among the best conductors, as already 

 noted, and therefore offer less resistance than non- 

 metals. Liquids, specially saline solutions, also con- 

 duct, but they always ofler more resistance than 

 metals. Thus, in a cell or in a battery from which 

 the electricity is conducted by wires to some apparatus, 

 there are manifestly two main sources of resistance. 

 There is, first, the resistance the current experiences 

 in passing through the liquid of the cell from one 

 plate to another. This is the internal resistance, 

 or the resistance of the element. But in passing 

 through the wires and through the apparatus that 

 may be in use, the current meets with further resis- 

 tance. This is the external resistance, or the resistance 

 of the external part of the circuit. Now, it is found 

 that the internal resistance is inversely proportional to 

 the size of the plates in the cell, and directly proportional 

 to their distance from one another; i.e. the larger 

 the plates the less the resistance, and the greater the 

 distance the greater the resistance, the conducting 



* Though this language is used, it is not to be supposed that 

 the electric current is a material thing, or that resistance is offered 

 by material obstacles. Part of the energy of the current is \ised 

 up in heating the conductor, and the enfeeblement of the current 

 from this cause comes under the head of resistance. 



