472 Sir Henry Gimynghame [Feb. 19, 



superincumbent mass of coal to fall. Here are two slides representing 

 coal cutters at work. 



[Five photographs of coal cutters and other machinery.] 



The future of coal mining, of course, lies in the use of machinery, 

 which both saves labour and also avoids many dangers. 



Having thus endeavoured to give an elementary idea of work in 

 a mine, I come to the main subject of my lecture, namely, the 

 dangers attendant upon it. 



If from 5 to 16 per cent, of fire-damp, which is a sort of coal 

 gas, is mixed with air and ignited, an explosion of more or less 

 violence takes place, but when the mixture is either too poor or too 

 rich in gas, it will not explode. 



[Experiment.] 



It is desirable that gas should never be allowed in a mine in a 

 proportion of more than about 2 per cent., witliout immediate means 

 being taken for its removal. 



The earliest mode of lighting in a mine was the simple expedient 

 of a taUow candle stuck into a lump of clay and dabbed on anywhere, 

 most often on to the front of the workman's hat. 



The dangers of gas explosions led to attempts to supersede the 

 use of naked Hghts. The first of these consisted of a steel wheel 

 turned by hand, against which a flint was pressed so as to emit a 

 shower of sparks. This gave a feeble light, but it was soon discovered 

 that it would ignite gas, and was therefore abandoned. 



The need for a safe lamp became imperative. In 1816 Sir 

 Humphrey Davy, Professor of Chemistry to this Institution, attacked 

 the problem, namely, to convey air to a light in such a manner that, 

 though the air was contaminated with gas, yet the flame of the lamp 

 would not be communicated to the gas outside. 



It first occurred to Davy to try a long tube as an inlet. This he 

 did with success, for it was found that a flame from an explosive 

 mixture would not, naturally, traverse a copper tube \ of an inch in 

 diameter. 



The reason of this apparently curious fact is, that the copper 

 sucks the heat away so fast, that the temperature of the flame which 

 impinges against it, is reduced to a point too low to burn. The 

 smaller the tube, the greater the effect. So that, if we took a sort of 

 network of very small bits of tube piled upon one another, you 



[Diagram.] 



would have, as it were, a flame-sieve. From this, it was but a step 

 to substitute a gauze, for it was found that flame would not pass 



