lupton: safety lamps. 
271 
conditions, be certainly extinguished ; and it has happened that all 
the lamps in a large colliery have been extinguished by a sudden 
blower of gas filling the mine with an explosive mixture This is an 
element of safety which the Davy lamp does not possess, and in 
consequence the Stephenson lamp has been very largely used ; it 
gives, however, a worse light than the Davy^ 
The Mueseler (see fig. 4) or Belgian lamp resembles a Clanny 
and differs from it only in having a metal chimney and flat gauze 
diaphragm at the top of the glass. This lamp has two advantages 
over the Clanny, it is safer, because the horizontal gauze and the 
chimney constitute minor lines of defence ; the chimney is a defence, 
because it is filled with the products of conbustion through which 
a flame will not pass under ordinary circumstances. The second 
advantage is that the lamp is extinguished when put into an explosive 
mixture, so that in the case of a blower all the lamps in a large mine 
have been extinguished. The Mueseler lamp has only one fault in 
the eyes of the workman, and that is that it goes out if held a little 
crooked. The Mueseler has come into very extensive use because it 
combines the safety of a Stephenson lamp with the good light 
of a Clanny. This lamp then seems prima facie to satisfy our 
requirements, and we will pause to enquire as to what are the circum- 
stances under which it is not safe. The lamp is not safe to use 
with a reduced flame when testing for gas, as it might cause an ex- 
plosion, the same as the Clanny, but it is safe for fire-trying with a 
full flame. 
Some of the lamps which I have named are safe in a rapid 
current of an explosive mixture. Thus if a Davy is in a current of 
400 feet per minute, it will explode the gas. A Clanny, a Stephen- 
son, and a Mueseler may explode the gas if the speed is 600 feet per 
minute. It very rarely happens that an explosive mixture travels 
through a mine at the speed of 400 or 600 feet per minute, but it 
often happens that a lamp is carried or moved at a very much greater 
speed, and therefore it is desirable to have a lamp that is safe at any 
speed. A man may travel as fast as a mile in ten minutes or 500 
feet per minute, and he may meet a current going at an equal speed , 
the current would, therefore, strike the lamp with a velocity of 1000 
