168 SAFETY LAMP. 



months together. It has been found that an uniform current of gas 

 existed for two years and a half in one of the mines. This gas, in the 

 state in which it issues from the coal, burns with a bright flame like 

 ordinary gas, but when united with a certain portion of atmospheric air' 

 the mixture becomes explosive, i. e., the whole volume of air, upon the 

 approach of a flame, suddenly catches fire, and goes off like gunpowder, 

 with a tremendous explosion. The frightful consequences of these ex- 

 plosions have been greatly lessened, and would, with care, be prevented 

 altogether, by the constant use of Sir Humphry Davy's 



SAFETY LAMP. 



That eminent man, by numberless experiments on the nature of fire 

 damp, and on the proportions with which it must be mixed with the air 

 of the atmosphere to be explosive, found that in respect of com- 

 bustibility, the fire damp differs most materially from the other common 

 inflammable gases, inasmuch as it requires a far higher temperature 

 before it can be set on fire ; an iron rod at the highest degree of red 

 heat, and at the common degree of white heat, did not inflame explosive 

 mixtures of the fire damp, and an explosion only took place when a 

 flame was applied. He also made the important discovery, that flame 

 will not pass through a tube with a small bore; and guided by this 

 principle, he was led through a train of ingenious experiments to the 

 construction of a lamp, which has saved already hundreds of lives, and 

 whose value is inestimable. Jt is very simple in its construction. It is 

 a lamp in which oil is burned, and there is a small bent wire, moved by 

 passing through a hole in the bottom, for trimming the wick. There is 

 also a cover of fine wire gauze, which is fastened upon the lamp, and 

 generally locked to prevent the miners taking it off, and this cover is 

 strengthened by upright wires twisted at the top to receive a ring for 

 carrying the lame. When the lamp is carried into a part of the mine 

 which is highly charged with fire damp, the flame of the wick begins to 

 enlarge, and the air, if it contain so much inflammable gas as to be highly 

 explosive, takes fire as soon as it has passed through the gauze, and 

 then burning within the lamp extinguishes the flame of the wick, by 

 cutting off all communication with the pure air of the atmosphere. 

 Whenever this appearance is observed, the miner must instantly 

 withdraw, for although the flaming gas within the lamp cannot pass 

 through the gauze so as to set fire to the explosive mixture outside, it 

 makes the wire gauze so hot that it would very speedily be wasted, and 

 a hole large enough to let the flame come cut would be burned. 



