462 DAVY. 



in spite of all preventives, and the destruction of a 

 hundred or more lives was not an unusual calamity. 

 Davy about the year 1815 turned his attention to the 

 subject, and after fully ascertaining that carburetted 

 hydrogen is the cause of the fire-damp, and finding in 

 what proportions it must be mixed with air in order to 

 explode (between six and fourteen times its bulk), he 

 was surprised to observe, in the course of his experi- 

 ments made for the purpose of ascertaining how the 

 inflammation takes place, that the flames will not pass 

 through tubes of a certain length or smallness of bore. 

 He then found that if the length be diminished, and the 

 bore also reduced, the flames will not pass ; and he fur- 

 ther found that by multiplying the number of the tubes, 

 their length may safely be diminished to hardly any- 

 thing, provided their bore be proportionally lessened. 

 Hence it appeared that gauze of wire, whose meshes were 

 only one twenty-second of an inch diameter, stopped 

 the flame, and prevented the explosion. The candle 

 or lamp being wrapt in such gauze, and all access to 

 the external air prevented except through the meshes, 

 it is found that the lamp may be safely introduced into 

 a gallery filled with fire-damp ; a feeble blue flame will 

 take place inside the gauze, but no explosion, even if 

 the wire be heated nearly red. 



The theory is, but it seems very questionable, that the 

 conducting power of the wire carrying off the heat pre- 

 vents a sufficient quantity reaching the explosive com- 

 pound. Subsequent inquiries seem to prove that 

 although in a still atmosphere of explosive gas the lamp 

 is a perfect protection, yet it does not prevent a cur- 

 rent of gas from penetrating to the flame and exploding. 



