SIR HUMPHRY DAVY ? S SAFETY-LAMP. 



All known bodies, when heated to a certain intensity, become 

 luminous. Thus iron, when its temperature is elevated, first 

 gives a dull red light, which becomes more and more white as the 

 temperature is increased, until at length it becomes as white as 

 the sun. Davy showed that gaseous substances are not exempt 

 from this law, and that name is nothing more than gas rendered 

 white hot. 



He further showed that if the gas thus rendered white hot be 

 cooled, it will cease to be luminous in the same manner, and from 

 the same cause, as would be the case with a red hot poker plunged 

 in water. 



He showed that the gas which forms flame may be cooled by 

 putting it in contact with any substance, such as metal, which is a 

 good conductor. 



Thus, if a piece of wire net- work, with meshes sufficiently close, 

 be held over the flame of a lamp or candle, it will be found that 

 the flame will not pass through the meshes. The wire will become 

 red hot, but no flame will appear above it. 



It is not, in this case, that the gas which forms the flame 

 does not pass through the meshes of the wire, but in doing so, it 

 gives up so much of its heat to the metal, that when it escapes 

 from the meshes above the wire, it is no longer hot enough to be 

 luminous. 



Sir Humphry Davy, in the researches which he was called to 

 make discovered this important fact, which enabled him to 

 explain the nature and properties of flame ; and having so dis- 

 covered it, he did not fail promptly to apply it to the solution of 

 the practical problem with which he had to grapple. 



This problem was, to enable the miner to walk, lamp in hand, 

 through an atmosphere of highly explosive gas, without the pos- 

 sibility of producing explosion. It was as though he were 

 required to thrust a blazing torch through a mass of gunpowder, 

 without either extinguishing the flambeau or igniting the powder ; 

 with this difference, however, that the gaseous atmosphere to 

 which the miner was often exposed was infinitely more explosive 

 than gunpowder. 



The instrument by which he accomplished this was as remark- 

 able for its simplicity as for its perfect efficiency. A common 

 lantern, containing a lamp or candle, instead of being as usual 

 enclosed by glass or horn, was enclosed by wire gauze of that 

 degree of fineness in its meshes which experiment had proved to 

 be impervious to flame. When such a lantern was carried into an 

 atmosphere of explosive gas, the external atmosphere would enter 

 freely through the wire gauze, and would burn quietly within the 

 lantern; but the meshes which thus permitted the cold gas to 



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