ELECTRICAL ADVANCE IN THE PAST TEN YEARS. 131 



the kinds of current; and they are referred to here solely to illustrate 

 the extreme flexibility of electrical work as lately developed. The 

 whole Niagara plant has grown into existence within the past five 

 years, and as a consequence of the technical advances within the 

 period of the past ten years. There are, however, in active operation, 

 besides the Magara power plant, several other water-power transmis- 

 sions, some of them far exceeding in distance that between Niagara 

 and Buffalo, and some in which the amount of power conveyed, as well 

 as the pressure of the current used upon the line, is much greater than 

 is yet to be found at Niagara. 



Electric transmissions are in particular favor in regions where the 

 cost of steam power, owing to dear fuel, is a stimulus to the utilization 

 of water powers which already exist or which are capable of develop- 

 ment. It is not surprising, therefore, that the far West should furnish 

 some of the most notable examples. 



No limit can as yet be definitely set as to the distance which can be 

 covered in an electrical transmission. The higher the voltage or elec- 

 trical pressure which may be found practicable, the greater the distance 

 which may exist between the transmitting and receiving machinery. So, 

 also, the higher the cost of fuel in a locality, the greater the distance 

 over which it is feasible to make the transmission. It may be said that 

 at present the range of distances is between 30 and 100 miles. 



It is interesting to compare the conditions in long-distance telephony 

 with those of a power transmission. With the former an exceedingly 

 feeble current is sent out; and though only a small percentage reach 

 the receiving telephone, still it may be sufficient to produce the sounds 

 of the voice with such distinctness as to enable them to be recognized. 

 To secure this result the long-distance telephone lines are made of heavy 

 copper wires, and the longer the distance to be covered the thicker 

 must be the line wire. 



The cost of the copper in the line becomes very heavy for great dis- 

 tances, over 1,000,000 pounds of copper being required for a single cir- 

 cuit from Boston to Chicago. In a power transmission, on the other 

 hand, the currents are of great pressure and sometimes represent thou- 

 sands of horsepower, and it is essential that in the transmission not 

 more than a certain percentage of the energy be lost. Thus in some 

 cases a 20 per cent loss would be too much to allow and in others a 25 

 to 30 per cent loss might not be inordinate. 



In this case, again, heavy copx)er wires are used for the lines, insu- 

 lated as well as possible; and the cost of the copper for obtaining con- 

 ducting power sufficient to prevent undue loss, other things being equal, 

 sets the limit of distance. In the telephonic transmission the percent- 

 age of loss is not important, provided the characteristics which represent 

 speech in the receiver are not lost, while in the power transmission the 

 percentage of loss is vital, as the object of the plant is simply to trans- 

 mit energy under economical conditions. 



