CHAP, in.] ELECTRICITY AND MAGNETISM. 137 



f tonal to the quantity of electricity that passes through it; 

 that is to say, is proportional to the strength of the 

 current while it passes. 



One weber^ of electricity in passing through the cell 

 liberates ^-^^> (or -0000105) of a gramme of hydrogen, 

 and causes AVI^ (or -00034125) of a gramme of zinc to 

 dissolve in the acid. 



II. The amount of chemical action is equal in each cell 

 of a battery consisting of cells joined in series. 



The first of these laws was thought by Faraday, who 

 discovered it, to disprove Volta's contact theory. He 

 foresaw that the principle of the conservation of energy 

 would preclude a mere contact force from furnishing a 

 continuous supply of current, and hence ascribed the 

 current to the chemical actions which were proportional 

 in quantity to it. How the views of Volta and Faraday 

 are to be harmonised has been indicated in the first 

 paragraph of this lesson. 



LESSON XV. Voltaic Batteries. 



167. A good Voltaic Battery should fulfil all or most 

 of the following conditions : 



1. Its electromotive-force should be high and con- 



stant. 



2. Its internal resistance should be small. 



3. It should give a constant current, and therefore 



must be free from polarisation, and not liable 

 to rapid exhaustion, requiring frequent renewal 

 of the acid. 



4. It should be perfectly quiescent when the circuit 



is open. 



5. It should be cheap and of durable materials. 



6. It should be manageable, and if possible should 



not emit corrosive fumes. 



1 For the Definition of the weber, or practical unit of quantity of electricity, 

 see Art. 323 



