ELEMENTARY LESSONS ON [CHAP. in. 



CHAPTER III. 



CURRENT ELECTRICITY. 



LESSON XIII. Simple Voltaic Cells. 



147. It has been already mentioned, in Lesson IV., 

 how electricity flows away from a charged body through 

 any conducting substance, such as a wire or a wetted 

 string. If, by any arrangement, electricity could be 

 supplied to the body just as fast as it flowed away, a 

 continuous current would be produced. Such a current 

 always flows through a conducting wire, if the ends are 

 kept at different electric potentials. In like manner, 

 a current of heat flows through a rod of metal if the 

 ends are kept at different temperatures, the flow being 

 always from the high temperature to the lower. It is 

 convenient to regard electricity as flowing from positive 

 to negative ; or, in other words, the direction of an electric 

 current is from the high potential to the low. It is 

 obvious that such a flow tends to bring both to one 

 level of potential. The " current " has sometimes been 

 regarded as a double transfer of positive electricity in 

 one direction, and of negative electricity in the opposite 

 direction. The only evidence to support this very un- 

 necessary supposition is the fact that, in the decom- 

 position of liquids by the current, some of the elements 

 are liberated at the point where the potential is highest, 

 others at the point where it is lowest. 



