ON EXPLOSIONS OF FIRE-DAMP IN COAL MINES. 
23 
place, extra precautions should be used. Also, when a safety- 
lamp is carried where firedamp is present, the flame elongates 
and takes a pale bluish hue, till the gas is present in quantity 
enough to cause explosion within the gau/e. These indications 
enable a trained eye to estimate to a very fair degree of approxi- 
mation the proportion of gas present. The observation of them 
partakes somewhat of the nature of playing with fire, and 
requires a cool head and steady hand, and a knowledge, which 
can be acquired only by practice, how far it is safe to go, and 
when it becomes necessary to withdraw or extinguish the light. 
A very beautiful and ingenious indicator has been invented by 
Mr. Ansell, the general principle of which is as follows : — A 
vessel full of air is separated from the impure atmosphere of 
the mine by a porous diaphragm. In virtue of the law of the 
diffusion of gases, air passes out and carburetted hydrogen 
passes in through the diaphragam ; but the latter, on account of 
its low specific gravity, is transferred in larger quantity than the 
former. Consequently the pressure within the chamber is in- 
creased, and either by the expansion of the elastic walls of the 
vessel itself, or by the raising of a column of mercury, an 
electric circuit is completed, and a telegraphic bell set ringing. 
If such instruments are placed at different points in the mine, 
and connected by wires with bells at some- central station, the 
presence of gas in dangerous quantity at any place is imme- 
diately pointed out, and the necessary orders may be at once 
issued. In another form of the instrument, intended to be 
carried about, the gas passes by diffusion into a sensitive ane- 
roid chamber, and moves an index in the same way as in the 
common aneroid barometer. Beautiful as these contrivances 
are, it is a question whether their construction is not too delicate 
to stand the rough life of a coal mine ; but fair and ample tmal 
ought certainly to be made of them. Their competency to 
detect the presence of gas has been proved by actual experi- 
ment, and the time may come — the average intelligence of 
the collier having been raised by education — when it will be 
possible to employ them as the inventor has suggested. 
And now comes the question. How is it that though science 
ha& worked so earnestly, and as it would seem so successfully, 
to put into the miner’s hands the means by which he may pro- 
tect himself from the dangers that beset him on all sides, the 
tale of lives lost year by year shows no signs of a decrease ? To 
anyone who has studied the Eeports of the Colliery Inspectors, 
the answer comes in no uncertain tone. The facts there col- 
lected show, without the possibility of a mistake, that a very 
large portion of the accidents ought never to have occurred, 
since they have been caused either by the incompetence of the 
managers or the foolhardiness of the men. 
