118 nature's flfctrades. 



speak while the operative who is sending 

 with the negative pole to line pulls more cur- 

 rent in the same direction through the line 

 whenever he closes his key. 



This may not be a strictly scientific state- 

 ment ; but, as long as we speak of a " cur- 

 rent " flowing from positive to negative poles 

 ( which is the invariable course electricity 

 takes), it is the way to look at the matter un- 

 destandingly. 



The short " resistance-coil " at each end, for- 

 tified by a " condenser " made of many leaves 

 of isolated tin-foil, to give it capacity, offers 

 precisely the same resistance to the current as 

 the 500 miles of wire line; so that the twin 

 currents that run around the differential mag- 

 net exactly neutralize each other and make no 

 effect in the office the message starts from; 

 while one of them takes to the earth, and the 

 other to the line to carry the message. 



This condenser is necessary, because the 

 short resistance-coil affects the current imme- 

 diately, while the long line with its greater 

 amount of metal does not give the same 

 amount of resistance till it is filled from end 

 to end, which requires a fraction of a second. 

 During this time, however, more current is 

 passing through the differential coil connected 

 with the line than through the short resist- 

 ance-coil; and the unequal flow causes the 

 relay armature to jump, or " kick." The con- 



