THE MINERAL DEPTHS 



the racking vibrations that exhaust the workmen, 

 and, like the air drills, sometimes cause serious dis- 

 eases. On the other hand the advocates of the pick 

 machines point out that they can be used in mines too 

 narrow for the introduction of chain machines. They 

 show also that there is a constant element of danger 

 from motor-driven machines in mines where the quan- 

 tity of gas present makes it necessary to use safety 

 lamps, on account of the sparking of the machines 

 which may produce explosions. Both these claims 

 are valid, but apply only to special cases, or to certain 

 mines, and do not affect the general popularity of the 

 chain machines. 



There are several different types of chain cutting ma- 

 chines, such as " long-wall machines," and " shearing 

 machines," but these need not be considered in detail 

 here. The general principle upon which they work is 

 the same as the ordinary chain machine, the difference 

 being in the method of applying it for use in special 

 situations. 



ELECTRIC LIGHTING OF MINES 



For many obvious reasons the ideal light for mining 

 purposes is one in which the danger from the open 

 flame is avoided, particularly in well-ventilated mines, 

 or mines under careful supervision, where the danger 

 from inflammable gases is slight. The incandescent 

 electric light, therefore, has become practically indis- 

 pensable in modern mining operations. For certain 

 purposes and in certain locations where an intense 



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