608 ELECTRICAL ENGINEERING 



drive can transmit say 300 kilowatts (about 400 horse-power) to a 

 distance of a few kilometers by its bodily movement at the rate of a 

 few meters per second. On the other hand, a quiescent electric cable 

 of copper, suspended on the insulators of a pole line, can transmit 

 3000 kilowatts to a distance of a few hundred kilometers, with about 

 the same efficiency. In the case of the mechanical transmission, the 

 wear and tear and depreciation of the steel cable is considerable. In 

 the case of the electric transmission, the wear and tear of the con- 

 ductor has never yet been detected. The depreciation is practically 

 limited to that of the poles, insulators, and mechanical supports. So 

 far as is yet known, an electric conductor does not wear out electric- 

 ally by the exercise of its functions. 



At the present time, the longest commercial electric power trans- 

 mission is in California, from de Sabla water-power house, in the 

 foot-hills of the Sierra Nevada, to Sausalito, opposite San Fran- 

 cisco, a distance of 232 miles (373 kilometers); while 7500 kilo- 

 watts (10 ; 000 horse-power) is regularly transmitted from Electra, 

 another water-power house in the Sierras, to San Francisco, a dis- 

 tance of 147 miles (236 kilometers). It would seem as if it were only 

 a question of time when every important waterfall shall be har- 

 nessed to turbines and dynamos for the transmission of solar energy 

 to the nearest mart. 



Up to the present time, the coal-supplies of the world have kept 

 us amply furnished with power at low rates. With coal averaging 

 say $2.25 per metric ton in the Eastern United States, the cost of 

 a kilowatt-hour at the steam-engine shaft during the working hours 

 of the year is from 1.75 cents in small plants to 1.33 cents in larger 

 plants, with good management and economy. It is estimated that 

 the world's total output of coal is approximately two millions of 

 , metric tons daily. At the present rapidly increasing rate of con- 

 sumption, the cost of coal delivery tends slowly to increase. Un- 

 less, therefore, discoveries are made of new available sources of 

 power, the value of solar power may be expected to appreciate. 

 The only solar engine of large power that has thus far been made 

 effective, or which promises to be effective in the near future, is 

 the waterfall. Already several hundreds of thousands of kilowatts 

 of the world's water-power are electrically converted from waste 

 to utility. In the single instance of Niagara Falls, about 100,000 

 kilowatts are already utilized, and plans now in progress promise 

 to develop a total of about 500,000 kilowatts more. This electrical 

 power is sold to consumers in the vicinity of the Niagara power- 

 house at about a quarter of a cent per kilowatt-hour, in large quan- 

 tities, continuously. 



One of the greatest advantages which electrical engineering has 

 rendered and is rendering to the people is in cheapening and accel- 



