THE MINERAL DEPTHS 



come the possibility of such forgetfulness or wilful dis- 

 obedience, it was found necessary to equip safety lamps 

 with locking devices, so that the miner had no means of 

 access to the open flame of his lamp once it had been 

 lighted. 



Since the time of the first Davy safety lamp there 

 have been numerous improvements in mechani- 

 cal details, although the general principle remains 

 unchanged. One of these improvements is a device 

 whereby the lamp, when accidentally extinguished, 

 may be relighted without opening it, and without the 

 use of matches. This is done by means of little strips 

 of paper containing patches of a fulminating substance 

 which is ignited by friction, working on the same prin- 

 ciple as the paper percussion caps used on toy pistols. 



But even the improved safety lamp seems likely to 

 disappear from mines within the next few years, now 

 that electricity has come into such general use. As 

 yet, however, no satisfactory portable electric lamp 

 or lantern has been perfected, such lamps being as a 

 rule too heavy, expensive, and unreliable. Even if 

 these defects were remedied, the advantage would still 

 lie with the Davy lamp, since the electric lamp, being 

 enclosed, cannot be used for the detection of fire damp. 

 But this advantage of the safety lamp is becoming less 

 important, since well-regulated mines are now more 

 thoroughly ventilated, and the danger from fire damp 

 correspondingly lessened. 



In some Continental mines the experiment has been 

 tried of constantly consuming the fire damp, before 

 it has had time to accumulate in explosive quantities, 



