200 On the Wire-gauze Lamps. 



The light of the miner's candle was - - 45 5, 



That of a lamp furnished with a tin plate reflector for di- 



minisiiing the circulation of the air, and facing a 



blower, was - _ _ _ 49. 



That of a single common lamp - - 3.0. 



That of a doubie copper wire lamp - - - 25. 



That of the steel mill, very unequal and uncertain ; but 



at its greatest intensity of hght - - - 25. 



It may be proper to observe, without reference to the supe:- 

 riority of light, that coals may be worked nearly twice as cheap 

 by the wire gauze safe lamp, as by the steel mill. 



The pleasure of seeing the wire gauze safe lamps in general 

 use amongst the miners, and adding to the security and happi- 

 ness of this useful class of men, amply repays me for the labour 

 of twelve months devoted to their cause, and for the anxiety 

 which I have often experienced during the progress of the in- 

 vestigation. 



Newcastle, Sept. 9, 1316. H. Davy, 



P. S.— I have shown in a paper printed in the Transactions of 

 the Royal Society, that the power of heated wire-gauze, to permit 

 the passage of the flame of coal-gas, is directly as the size of the 

 apertures, and, to a certain extent, as the velocity of the current: 

 I say to a certain extent, because, by a current of a certain velo- 

 cily, flame is extinguished. A very slight motion will pass the 

 flame of coal-gas through wire-gauze having less than 400 

 apertures to the square inch, even when it is heated to dull red- 

 ness ; but a very strong current and an ignition above redness, 

 visible in day-light, is required to pass the same flame through 

 wire-gauze having above 700 apertures to the scjuare inch : and 

 I have never been able to pass the flame of coal-gas or any car- 

 bonaceous flame through wire-gauze having more than IGOO 

 apertures to the square inch, by any means. 



The experiments above detailed on the blower, are tlie first I 

 have made upon currents of fire-damp . They prove what I had 

 inferred from its othe-r properties, and they ofl^er simple mean§ 

 of rendering wire-gauze lamps perfectly safe against all circum- 

 stances, however extraordinary and unexpected, and of placing 

 their security above the possibility of doubt or cavil. 



XLI. On 



