64 HEROES OF INVENTION AND DISCO VER Y. 



Meamvhile his attention had been attracted to another 

 subject of the greatest practical importance — the possibility of 

 preventing the destructive explosions in coal-mines occasioned 

 by the fire-damp, or inflammable gas, which is found in many 

 parts of them. By a series of experiments, Davy found that 

 this dangerous gas, which was known to be nothing more than 

 the hydrogen of the chemists, had its explosive tendencies very 

 much restrained by being mixed with a small quantity of 

 carbonic acid and nitrogen (the ingredient which, along with 

 oxygen, forms atmospheric air) ; and that, moreover, if it did 

 explode when so mixed, the explosion would not pass through 

 apertures less than one-seventh of an inch in diameter. Pro- 

 ceeding, therefore, upon these ascertained facts, he contrived 

 his celebrated Safety Lamp. It consists of a small light, fixed 

 in a cylindrical vessel, which is everywhere air-tight, except in 

 the bottom, which is formed of fine wire gauze; and in the 

 upper part, where there is a chimney for carrying off the foul 

 air. The air admitted through the gauze suffices to keep up 

 the flame ; which, in its combustion, produces enough of car- 

 bonic acid and nitrogen to prevent the fire-damp, when inflamed 

 within the cylinder, from communicating the explosion to what 

 is without. The heretofore destructive element, thus caught 

 and detained, is therefore not only rendered harmless, but 

 actually itself helps to furnish the miner with light, the whole 

 of the interior of the cylinder being filled with a steady green 

 flame, arising from the combustion of the hydrogen, which has 

 been admitted to contact v/ith the heat, but cannot carry back 

 the inflammation it has received to the general volume without. 

 Armed with this admirable protection, therefore, the miner 

 advances without risk, and with sufficient light to enable him 

 to V/'ork, into recesses Vi^liich formeily he could not have dared 



