HISTORY AND PROGRESS. 105 



the ordinary means of suspension, a considerable decrease in 

 the intensity of the currents which leave the transmitting 

 station, occurs before they reach their destination ; and this 

 waste it is impossible to prevent. If no other causes were 



Fig. 56. 



present, the resistance of the wire, combined with the fact 

 that no absolute insulation, even under the most favourable 

 conditions, exists, would alone put a limit to the length of 

 line on which it would be possible to work direct. But this 

 limit is, in practice, very considerably contracted, as the 

 methods of insulatiom employed are always liable to tem- 

 porary derangements by dampness of the atmosphere, dirt, 

 and other causes, which account for the innumerable little 

 shunts that a current finds all along the line, and by which 

 it tries its utmost to get back, without going to the end of 

 the line. 



Imagine a long line between two distant stations, A and E, 

 with three intermediate stations, B, C, and D, also far apart. 

 If A wanted to send a message to E, the line being too long 

 and the leakage of the current too great, it would have to 



