208 Mr. William Henry Preece [Feb. 10, 



gas, is marsh gas (C H4). It oozes out gently from the exposed seam, 

 or sometimes it bursts out through some fissure with great force, forming 

 what are called " blowers." If it be mixed with air, in the propor- 

 tion of from 5 to 9 per cent, of gas, it becomes highly explosive, and 

 is the prime cause of those fearful disasters that have made coal 

 mining so terrible. 



In gasless mines candles always have been and still are used, but 

 in early days, in foul places, men had frequently to work in the dark, 

 or to be content with the feeble illumination of the phosphorescence 

 of decaying fish. It is remarkable how the eye adapts itself to feeble 

 light, and in the Cimmerian darkness of a coal-mine even phospho- 

 rescence has a useful illuminating effect. In many places they used 

 the steel mill, a disc of steel rotated rapidly against flint, giving light 

 by the shower of sparks thrown down. It is most remarkable that no 

 scientific thought was devoted to this subject until 1815. In 1813 

 Dr. Clanny, of Newcastle, had devised a very poor lamp, the air to 

 support which was driven by bellows through water ; but in 1815 

 Sir Humphry Davy devoted his powerful mind and skilful hands to 

 solve the question, and speedily invented in this very Institution his 

 immortal safety lamp. It is a remarkable coincidence that in the 

 same month another powerful but untutored mind, by strong observant 

 pow'crs and pure mechanical reasoning, had arrived at very nearly the 

 same result ; and even to this day the affectionate remembrance and 

 name of the eminent Northumbrian brakesman, George Stephenson, 

 is maintained by the use of the " Geordie," in his old home, the Kil- 

 lingworth Colliery. 



Davy's classical paper was read before the Royal Society, on 

 November 11, 1815, and was entitled " On the Fire Damp of Coal 

 Mines; and on Methods of Lighting the Mine so as to Prevent 

 Explosion." He showed that flame would not pass through small 

 tubes and apertures, and how in comparatively still air, however 

 charged with gas, a wire gauze surrounding the flame so reduced the 

 temperature by radiation that explosion was impossible. Ingress of 

 air and egress of products of combustion are resisted. He showed that 

 a flame so protected gave immediate intimation of the presence of gas 

 by burning dimly, and by becoming capped with a blue flame, or 

 aureole, that though the wire gauze became redhot, it still radiated 

 away the heat sufiiciently to prevent its reaching the temperature 

 point of explosioD. He also pointed out, which has been strangely 

 neglected, until enforced recently by the Eoyal Commissioners on 

 Accidents in Mines, that it failed to act in a current of air, but that 

 this effect of currents could be diminished by shielding or protecting 

 the inlet of air. 



The main principle discovered by Davy is the basis of all safety 

 lamps burning oil or spirit, but several departures in form have been 

 proposed at different times. The '* Geordie " is in reality a Davy 

 lamp with a glass shield. The " Jack " lamp is a Davy in a tin can. 

 The " Clanny " is a Davy lamji with the flame portion surrounded 



