CHAP, in.] ELECTRICITY AND MAGNETISM. 



as the resistance of the circuit; or, in other words, any- 

 thing that makes the E.M.F. of the cell greater will 

 increase the strength of the current, while anything that 

 increases the resistance (either the internal resistance in 

 the cells themselves or the resistance of the external 

 wires of the circuit) will diminish the strength of the 

 current. (See further concerning Ohm's Law in Lesson 

 XXIX.) 



Now the internal resistances of the cells we have 

 named differ very , greatly, and differ with their size. 

 Roughly speaking we may say that the resistance in a 

 Daniell's cell is about five times that in a Grove's cell of 

 equal size. The Grove's cell has therefore both a 

 higher E.M.F. and less internal resistance. It would 

 in fact send a current about eight times as strong as 

 the Daniell's cell of equal size through a short stout 

 wire. 



181. We may then increase the strength of a battery 

 in two ways : 



(1) by increasing its E.M.F. 



(2) by diminishing its internal resistance. 



The electromotive -force of a cell being determined 

 by the materials of which it is made, the only way to 



increase the total E.M.F. of a battery of given materials 

 is to increase the number of cells joined in series. It is 



