CHAPTER II. 



CURRENT ELECTRICITY. 



Potential. When two metals are placed in con- 

 tact there ensues a disturbance of their electrical 

 equilibrium. This disturbance is called a " difference 

 of potential." Thus, when zinc is placed in contact 

 with copper, or silver, or platinum, etc. , this difference 

 results, the zinc being at the higher potential, and the 

 copper, silver, or platinum at the lower. " Potential " 

 may be compared to "level." Water at a high level 

 inevitably tends to seek the lowest level ; and, con- 

 sequently, if it can find a channel, there will ensue a 

 flow until the place of zero has been reached. While 

 the water is at the high level it has the power of per- 

 forming work, i.e. it has "potential." In passing 

 from the higher to the lower level the water may per- 

 form work, but when it reaches the lowest level it has 

 lost all power of doing work, and is at zero of potential. 

 Similarly when two bodies have different electric 

 potentials, or two parts of the same body are at 

 different potentials, there is a tendency for a move- 

 ment from, the place of high to that of lower potential. 

 This movement is the so-called electric current, and it 

 is for the purpose of bringing both bodies to the same 

 potential. In the passage from a higher to a lower 

 potential work can be done. In fact, the " difference 

 of potential" is estimated by the amount of work 

 done in carrying each unit of electricity from the one 

 position to the other. It is necessary to observe that 

 though the phrase " current of electricity" and the 

 simile of water at different levels, have been used, they 

 are not meant to imply an actual transference of 



