THE ELECTRIC TELEGRAPH. 



contacts and separations, would also take place a hundred times 

 in a second. 



The existence of the current established in this case is inde- 

 pendent of the length of the wires P p and N n. Whether their 

 length be 10 feet, 10 miles, or 100 miles, the current will still 

 flow upon them when their extremities p and n are brought into 

 contact. The only difference will be, that the intensity of the 

 current will be less in the same proportion as the length of the 

 wires is augmented. 



23. There is another condition of great importance, whether 

 regarded theoretically or practically, 'on which the current will be 

 established and maintained. 



Instead of bringing the wires P p and N n into contact, let 

 them be continued downwards, as represented in fig. 2, and con- 

 nected with two plates of metal p' and n' t buried in the earth, or 



with masses of metal or other good conducting body of any form 

 whatever thus buried. In that case the current will be esta- 

 blished as before, flowing along the wire soldered to the copper 

 from P to p' and along that soldered to the zinc from n' to N. 



Thus, in both cases the current starts from the copper, and, 

 following the course of the wires, returns to the zinc. In the 

 former case, however, it is continuous ; but in the latter it is 

 apparently broken, terminating at p', and recommencing at n'. 

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