THE CONQUEST OF NATURE 



light is desirable and where there is no danger from 

 combustible gases, arc lights are used to a limited ex- 

 tent. But there is constant danger from the open 

 flame in using such lights, and also from the connecting 

 wires leading to them. Furthermore, such intense 

 light is not usually necessary in the narrow passages 

 of the mine. 



To be sure, there is a certain element of danger even 

 with incandescent lights on account of the possibility 

 of breakage of the globes, and of short-circuiting where 

 improper wiring has been done. To overcome as 

 much as possible the dangers from these sources, spe- 

 cial precautions are taken in wiring mines, and special 

 bulbs are used. In general the incandescent lamps 

 as used in mining are made of stout round bulbs of 

 thick glass which are not likely to crack from the effects 

 of water dripping upon them while heated. As a 

 further protection it is customary to enclose the bulbs 

 in wire cages. It is also customary to use low-current 

 lamps with a rather high voltage, although this must 

 be limited, as excessive voltage may in itself become 

 a source of danger. 



[270] 



