1909] on Means of Saving Life in Coal Mines. 473 



though a gauze made of sound iron or copper wires 28 to the inch. 

 This experiment is easy to show. Here I have a hand screen made 

 of iron wire gauze 30 meshes to the inch, and you see that it is 

 practically impossible to get the flame through it. 



[Experiment.] 



The lamp as designed by Davy was of the form shown here, and 



[Davy lamp.] 



I am enabled to exhibit the actual lamps used by Sir Humphrey Davy 

 in his experiments, and which have been preserved here as mementos 

 of that distinguished discoverer. 



The Davy lamp is now provided with a glass, and the gauze 

 screened by an iron bonnet, to prevent accidental injury. 



A lamp easily goes out in a mine if you carry it carelessly. The 

 question then arises, how is it to be relit without using a naked flame 

 in the mine. Some are reht by an electric spark got from an electric 

 machine in the mine, so arranged that while the lamp is being lit it is 

 enclosed in an airtight iron chamber. Some again are self-lighting. 



Here is a Wolf self-lighting lamp, such as are used in Germany. 



[Experiment.] 



When air containing gas surrounds a flame, a peculiar appearance 

 is given to it. When the flame of a common lamp is turned very 

 low and gas is present, a faint sort of halo is seen over the flame. 

 The diagram shows the appearances of the flames. Here I have a 



[Diagram.] 



lamp placed in a glass box to which gas can be admitted. You can 

 see when the gas percentage rises, the gradual rise of the flame. 



[Experiment.] 



The duty of repeatedly testing for gas is of course incumbent on 

 the officials in a mine, and when gas is seen the men should at once 

 be withdrawn and the ventilation increased so as to clear it away. 



Outbursts of gas called blowers occasionally defy even the greatest 

 precaution. 



In the model of working coal the position Avas shown for the 

 hole in which the explosive is put to bring down the coal. This 

 operation of blasting is called " firing a shot." The best explosive 



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