THE CONQUEST OF NATURE 



for fastening to the floor and roof, although the heavier 

 types are sometimes mounted on trucks. The motor, 

 which is not much larger or heavier than an ordinary 

 fan motor, is fastened to the upright and is from four 

 to six horse- power. This connects with a flexible 

 wire which transmits the power from the generating 

 station, frequently several miles away. The auger, 

 which is about the largest part of the machine and en- 

 tirely out of proportion to the little motor that drives 

 it, is simply a long bar of steel, twisted spirally at the 

 cutting-end like an ordinary wood auger. 



From the workman's standpoint these rotary drills 

 are infinitely superior to reciprocating or percussion 

 drills, where the constant jarring of the machine, be- 

 sides being extremely tiresome, sometimes produces 

 the serious disease known as neuritis. Various means 

 have been attempted to prevent this, such as by over- 

 coming the jar in a measure by flexible levers which 

 do not transmit the vibrations to the hands and arms; 

 but such attempts are only partially successful, and 

 a certain amount of jarring cannot be avoided. In 

 the rotary electric drills there is none of this, the work- 

 men simply controlling the drill and the motor with 

 levers, and receiving at most only a slight jar from the 

 vibrations of the auger. 



TRACTION IN MINING 



In recent years electric traction engines for use in 

 mines have been rapidly replacing horse- and mule- 

 power, and have become important economic factors 



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