lupton: satety lamps. 
269 
in effect a Davy lamp, thougli it may be with improvements added to 
it. 
I do not wish it to be supposed that I ignore the invention of 
George Stephenson, who invented a safety lamp at the same time that 
Davy invented his. Stephenson's invention had merit, but the 
merit was not equal to Davy's, because whilst the Davy lamp is and 
has been generally used, and is by some, even at the present day, 
considered to be unsurpassed for general utility, the Stephenson 
invention has never been practically used, except when put inside a 
Davy lamp. I will now briefly describe the Davy lamp, as a founda- 
tion for the description I propose to give of the various modifications 
and improvements, to which the time at my disposal will permit me 
to refer : — The Davy (see fig. 1) is an oil lamp, of which the flame is 
covered with a wire gauze cylinder; under ordinary conditions flame 
will not pass through this gauze, it is made of woven wires, the wires 
about l-50th of an inch in diameter, and 28 of these wires are laid 
paralled in an inch of warp, and the same number in the weft. This 
gauze constitutes a metallic case with perforations, and the case might 
be made of plate iron perforated with holes, this would make a lamp 
as safe as wire gauze when in good order, but it would be more easily 
broken; it would be more costly, and give less light. When flame is 
brought into contact with the gauze the gas passes through the 
apertures, but is cooled by the contact with the wires below the point 
of ignition, so that the flame does not pass ; hence a flame inside the 
lamp does not pass through and ignite gas on the outside ; and even 
when the gauze is very hot the same effect is produced, because the 
heat of a flame is so intense that very hot wire is cool by comparison. 
A lamp covered with this wire gauze may be safely carried through a 
mine filled with an explosive mixture, and may be used to detect 
the presence of inflammable gas, without danger to the fire-trier. 
When put into a place containing two per cent, of gas, if the flame 
is drawn down, a blue cap may be seen over the lamp flame, and the 
more the gas the bigger the blue cap ; but if there is eight per cent, 
of gas it will explode inside the lamp, but no harm ensues. The lamp 
has been used by hundreds of thousands of miners without accident, 
in other cases accidents have occurred. 
