ON EXPLOSIONS OF FIRE-DAMP IN COAL MINES. 
21 
known as “ blowers ” are liable to occur, because the discharge 
of gas from these is so sudden and so enormous as to overpower 
the most plentiful and perfect ventilation. In nearly all coals 
there is a risk, and in some a certainty, of meeting with these 
blowers, and for perfect security we must find some means of 
removing the danger arising from them. This is done by em- 
ploying what are known as “ safety-lamps,” that is, lamps 
which may be carried into an explosive mixture of carburetted 
hydrogen and air without firing the compound. The principle 
on which they depend was discovered independently about the 
same time by Sir H. Davy and Greorge Stephenson, and is as 
follows : — It was found that if a lamp or candle be enclosed in 
an envelope of fine wire gauze, containing not less than 600 
holes to the square inch, any explosions which take place 
within the envelope cannot be communicated to the gas out- 
side, and that the flame cannot pass through the gauze except 
under pressure.* In Davy’s original lamp the light is simply 
enclosed in a cylinder of this gauze, but this arrangement has 
a somewhat feeble illuminating power. Modifications have 
been made by the introduction of glass, which give a better 
light ; and other contrivances have been proposed for increas- 
ing the draught, and thus obtaining a similar result. The prin- 
cipal forms of safety-lamp are well described in the “ Eudi- 
mentary Treatise on Coal and Coal Mining,” by Mr. War- 
rington Smyth (Lockwood & Co., 1872). 
Unluckily, when perfect ventilation and an efficient safety- 
lamp have been provided, the colliery manager’s cares are not 
at an end. The working collier is proverbially reckless, and 
nothing can prevent him from opening his lamp, if he can, to 
get a better light for his work, to light his pipe, or even 
sometimes from foolhardiness. Lamps are locked before being 
given into the men’s hands, and then the men carry keys. 
Lamps are constructed which go out directly they are opened, 
and then .the men take down lucifers and light them again. 
Lamps have been devised which are locked with a plug of lead, 
on which a device is punched, and which cannot be opened 
without breaking the plug ; and some such troublesome pre- 
caution, it seems, must be adopted, if tampering with the 
lamp is to be put an end to. The latest contrivance is a lamp 
which is closed by a steel spring, and can only be opened by 
the action of a very powerful magnet on the spring. The 
magnet is kept in the custody of the head manager, and as it 
is obliged to be a far more powerful one than the colliers are 
likely to be able to obtain, this plan, if it succeed in other 
respects, seems likely to be effective. 
* For an explanation of the physical reason of these facts, see Tyndall’s 
Heat as a Mode of Motion,” p. 240. 
