38 THOMAS COMMERFORD MARTIN 



The profitableness of American mines and the sources of 

 national wealth have thus been enormousty increased. 



The number of mines in the United States reporting 

 electric power in 1902 was 802, with a total of 154,050 horee- 

 power. By far the larger proportion of these — namely, 688, 

 with a total of 130,494 horsepower — operated their own plants. 

 There were 131 mines, with a total of 23,556 horsepower, 

 which rented power, but of these mines 17 owned power also. 

 It will be gathered from these figures that the 130,494 horse- 

 power, even if it represents the total current generating capac- 

 it}^, shows a considerable application of electric power; but it 

 should probably be doubled in order to ascertain the capacity 

 of motors installed and using such current. It is a fact well 

 known in electrical plants that motor capacity far beyond the 

 actual current capacity of the generating plant can be in- 

 stalled, for the reason that the consumption of current is 

 variable and intermittent, it being highly improbable that all 

 the consuming apparatus will take full current from the lines 

 at the same time. It is assumable that in a great many in- 

 stances these plants furnish also considerable current for 

 lighting purposes. With regard to the rented power, it is 

 probable that it is employed almost altogether to drive motors, 

 a very small proportion of it representing electric lighting. 

 Mines in which the operations are so small as not to necessitate 

 the installation of a separate plant are, it is assumed, operated 

 largely by single shifts or during daylight hours ; so that while 

 some lighting would be needed, the consumption of current 

 would be quite small in proportion to the consumption for 

 hoists, pumps, and other motor driven mechanism. 



Four fifths of the electric power reported was concen- 

 trated in three industries — coal mining, cement working, and 

 the gold and silver industry. By far the largest item is that 

 of bituminous coal mining, such mines, numbering 309, report- 

 ing electric power with a total of 68,139 horsepower; and these 

 figures must be supplemented by those for anthracite coal 

 mining, with 17 plants, reporting 5,755 horsepower. It will 

 be seen that those two groups alone represent nearly one half 

 of the total horsepower. 



