THE MINERAL DEPTHS 



ful expenditure of energy. The modern method of 

 ventilating is by means of rotary fans, the electric fan 

 having practically solved the problem. The air cur- 

 rents established by such fans are controlled either by 

 the doors in the passages, or by means of auxiliary fans. 

 In addition, jets of compressed air are sometimes used, 

 and have become very popular. 



Another important problem that constantly confronts 

 the mining engineer is that of drainage. Mines are, 

 of course, great reservoirs for the accumulation of 

 water, which must be drained or pumped out continu- 

 ally; and as the shafts are sunk deeper and deeper it 

 becomes increasingly difficult to raise the water to the 

 surface. Special means and machinery are employed 

 for this purpose which will be considered more in detail 

 in a moment. 



ELECTRIC MACHINERY IN MINING 



Electricity is, of course, the great revolutionary fac- 

 tor in modern mining. There is scarcely a department 

 of mining in which electric power has not wrought 

 revolutionary changes in recent years; and the sub- 

 ject has become so important and so thoroughly spe- 

 cialized as to " create a literature and a technology of 

 its own." From the electric drill, working hundreds of 

 feet below the surface of the earth, to the delicate test- 

 ing-instruments in the laboratory of the assaying offices, 

 the effect of this electrical revolution is being felt 

 progressively more and more every year. 



Moreover, electricity, on account of its transmuta- 



[253] 



