260 LIGHT SCIENCE FOR LEISURE HOURS. 



fast as it passes within the wire cylinder, is ignited and 

 burns within the gauze. Thus the light now given out 

 by the kmp is no longer that of the comparatively 

 brilliant oil flame, but is the light resulting from the 

 combustion of carburetted hydrogen, or ' fire damp,' 

 as it is called ; and every student of chemistry is 

 aware that the flame of this gas has very little illu- 

 minating power. 



So soon as the miner sees the flame thus enlarged 

 and altered in appearance he should retire. But it is 

 not true that explosion would necessarily follow if 

 he did not do so. The danger is great because the 

 flame within the lamp is in direct contact with the 

 gauze, and if there is any defect in the wire-work, 

 the heat may make for itself an opening which 

 though small would yet suffice to enable the flame 

 within the lamp to ignite the gas outside. So long, 

 however, as the wire-gauze continues perfect, even 

 though it become red-hot, there will be no explosion. 

 No authority is required to establish this point, which 

 has been proved again and again by experiment ; but 

 I quote Professor Tyndall's words on the subject to 

 remove some doubts which have been entertained on 

 the matter. ' Although a continuous explosive atmo- 

 sphere,' he says, 'may extend from the air outside 

 through the meshes of the gauze to the flame within, 

 ignition is not propagated across the gauze. The 

 lamp may be filled with an almost lightless flame ; 

 still explosion does not occur. A defect in the gauze, 

 the destruction of the wire at any point by oxidation 



