THE SAFETY-LAMP. 287 



ensue, since the flame can. be forced mechanically 

 through the meshes, though it will not pass through 

 them when it is burning in the ordinary way. Now, 

 of course no miner who had been properly instructed 

 in the use of the safety-lamp would commit such a 

 mistake as this. But it happens, unfortunately, that 

 sometimes the fire-damp itself forces the flame of the 

 lamp through the meshes. The gas frequently issues 

 with great force from cavities in the coal (in which 

 it has been pent up), when the pick of the miner 

 breaks an opening for it. In these circumstances an 

 explosion is inevitable, if the issuing stream of gas 

 happen to be directed full upon the lamp. Fortu- 

 nately,, however, this is a contingency which does not 

 often arise. It is one of those risks of coal-mining 

 which seem absolutely unavoidable by any amount of 

 care or caution. It would be well if it were only such 

 risks as these that the miner had to face. 



Another peculiarity sometimes noticed when there 

 is a discharge of fire-damp is worth mentioning. It 

 happens, occasionally, that the light will be put out 

 owing to the absolute exclusion of air from the lamp. 

 This, however, can only happen when the gas issues in 

 so large a volume that the atmosphere of the pit be- 

 comes irrespirable. 



With the exception of the one risk which we have 

 pointed out above, the Davy lamp may be said to be 

 absolutely safe. It is necessary, however, that caution 



