ELECTROMOTIVE FORCE. 169 



poles are connected together by a closing arch, it finds 

 expression in the current which it generates in this 

 arch. 



Supposing that the two metals contained in the 

 fluid did not protrude from the latter, but were in 

 contact with each other within the fluid, then it is 

 evident that the apparatus would be closed in this case 

 also, but the closing arch would then lie within the 

 fluid. Through this the current must pass from the 

 copper to the zinc, and from the zinc to the copper 

 through the fluid. That this is really the case can 

 easily be shown, for on the immersed metallic surfaces 

 globules are seen to be generated, due to the gases 

 generated by the electric current by the separation of 

 the water into its constituent parts, hydrogen being 

 found at the copper, oxygen at the zinc point. In this 

 case, therefore, the apparatus is in itself closed. No 

 external closing-arch is present, the existence of a mag- 

 netic current at which can be indicated by means of a 

 magnetic needle. Yet with a multiplier it is possible 

 to show the currents circulating in the fluid, and in 

 the immersed metals ; this may be done by a principle 

 spoken of as the distribution of electric currents. 



Let us assume that an apparatus k is not directly 

 closed by a closing-arch, but that from each pole passes 

 a wire which touches the conductor, the form of which 

 does not matter, shown in fig. 40 at two points, A B. 

 It can be shown that the electric currents pass in this 

 case through the body, but distribute themselves, not 

 merely in straight lines connecting A and 5, but 

 throughout the body, so that they represent a number 

 of lines of conduction, all of which meet together at 

 the points A and B, where the electric currents enter 



