VENTILATION AND LIGHTING lU'KlNG < < NSTKUCTION 297 



LIGHTING. 



The object and necessity of a perfect lighting of the tunnel- 

 workings during construction are so obvious that they need not 

 be enlarged upon. Comparatively few tunnels require lighting 

 after completion ; and these are generally tunnels for passenger 

 tnttlic under city streets, of which the Boston Subway is a rep- 

 resentative American example. Considering the methods of 

 lighting tunnels during construction, we may, for sake of con- 

 venience, chiefly, divide the means of supplying light into (1) 

 lain}** and lanterns usually burning oil ; (2) coal-gas lighting; 

 (3) acetylene gas lighting; and (4) electric lighting. 



Lamps and Lanterns. Lamps and lanterns are commonly 

 employt-d by engineers for making surveys inside the tunnel, and 

 to light the instrument For ranging in the center line, a con- 

 venient form of lamp consists of an oil light inclosed in glass 

 chimney covered with sheet metal, except for a slit at the fnnit 

 and l>ack through which the light shines, and on which the 

 observer sights his instrument. To direct the operations of his 

 rod men the engineer usually employs a lantern, either with 

 white or colored glass, much like the ordinary railway train- 

 man's lantern, which he swings according to some prearranged 

 code of signals. 



Lamps and lanterns are used by the workmen both for sig- 

 naling and for lighting the woi kings. For signaling purposes 

 red lanterns are usually placed to denote the presence of unex- 

 ploded blasts or other points of possible danger; and colored or 

 \\liite lights are usually placed on the fr<>nt and rear of spoil 

 and material trains. For lighting purposes, two forms of lamps 

 are employed, which may l>e somewhat crudely designated as 

 lamps for individual use and lamps for general lighting. Indi- 

 vidual lamps are usually of small size, and burn oil; they may 

 l>e carried in front of the miner's helmet, or be fixed to stand- 

 ards, which can be set up close to the work being done by each 



