CHAP, vi.] ELECTRICITY AND MAGNETISM. 307 



CHAPTER VI. 

 MEASUREMENT OF CURRENTS, ETC. 



LESSON XXIX. Ohm's Law and its Consequences. 



345. In Art. 180 the important law of Ohm was 

 stated in the following terms : The strength of the 

 current varies directly as the electromotive -force, and in- 

 versely as the (total) resistance of the circuit. 



Using the units adopted by practical electricians, and 

 explained in Art. 323, we may now restate Ohm's law in 

 the following definite manner : The number of webers- 

 per-second of current flowing through a circuit is equal to 

 the number of volts of electromotive-force divided by the 

 mimber of ohms of resistance in the entire circuit. Or, 



Current = Electromotive-force 

 Resistance 



c -2 



~ R* 



In practice, however, the matter is not quite so simple, 

 for if a number of cells are used and the circuit be made 

 up of a number of different parts through all of which 

 the current must flow, we have to take into account not 

 only the electromotive-forces of the cells, but their resist- 

 tances, and the resistance of all the parts of the circuit. 

 For example, the current may flow from the zinc plate of 

 the first cell through the liquid to the copper (or carbon) 



