Niagara Falls 

 1894 passing through any given resistance varies as the square of the 



Le Sueur i. 



voltage. 



The chief difficulty to be met in such line construction is that 

 of efficiently insulating the wires. If any one attempted to use 

 a line insulated merely as an ordinary telegraph line is, there 

 would be an enormous loss, amounting practically to the whole 

 of the transmitted current, in moist weather, by leakage over the 

 damp surface of the glass or other insulators. The remedy for 

 this leakage would, however, be a comparatively simple matter 

 by means of well-known oil-holding arrangements for the insu- 

 lators were it not for the further fact that it is imperatively neces- 

 sary not to have the two wires, the going and return ones, farther 

 apart than can not be avoided on account of what are known as 

 the effects of self-induction. The wires strung on telegraph poles 

 would have to be so far apart in order to insure their never, by 

 any possibility, coming in contact, that the self-induction losses 

 would make that method impracticable. 



The evil effects of self-induction are directly proportional to 

 the number of alternations of the current in a given time, and 

 consequently the twenty-five-period current adopted for the 

 Niagara Falls work is highly advantageous from this point of 

 view. 



The so-called " skin-resistance " of an alternating current cir- 

 cuit is, in brief, due to the fact that an alternating current pene- 

 trates only a short distance into the body of the metal of which 

 the carrying wire is composed, instead of, as in the case of a 

 direct current, flowing across the whole cross-section of the wire 

 in an even manner. This also is less serious the lower the 

 periodicity. 



The form decided on in which to construct the conveying lines 

 is that of a conduit or subway of large proportions. One which 

 has been already constructed for a length of half a mile is as 



960 



