22 
POPULAK SCIENCE KEYIEW. 
A probable cause of accidents which we can only hint at 
here is the spontaneous combustion of the waste coal left in 
the goaf ; and it is also highly likely that some explosions have 
been caused by blasting in fiery pits. 
It is further to be noted, that even the most perfect safety- 
lamp requires occasionally the utmost caution in using it. In 
a fiery atmosphere the combustion and explosion of gas within 
the lamp sometimes raises the gauze to a red-heat, and in this 
way sets light to the explosive mixture outside. It has also 
been repeatedly proved by experiment that no lamp is safe in 
a strong current of air. The velocity necessary to cause an 
explosion varies with different forms of lamp, but all that have 
been yet devised blow up sooner or later, if the force of the 
draught in which they are placed is gradually increased.* 
Science has therefore still something further to do for the 
collier in the matter of lighting him at his work ; and the 
most promising quarter, perhaps, to which the would-be 
inventor can turn his attention is the electric light. If this 
could be produced cheaply and in a portable form, we should 
have in it all the conditions of perfect safety ; for the light 
may be completely cut off from the explosive atmosphere by 
surrounding it with a glass globe, and a cage of a few iron bars 
would guard against any risk of fracture to the glass. Even 
now it seems that this source of light might be usefully em- 
ployed in these exceptional cases, like the first opening out of 
a colliery after an explosion, when much of the work has to be 
done in the dark. A beam of parallel rays sent down the shaft 
by an electric lamp at the top would have intensity enough to 
allow of its being reflected by mirrors into the workings, and 
would make the task of beginning to open out a wrecked col- 
liery easier and more expeditious. And as soon as a cheap 
galvanic battery is invented, there seems to be no reason why 
we should not light our collieries with a brilliancy undreamed 
of now, and at the same time get rid of all risk of explosion. 
We have not yet said anything about the means of detecting 
the presence of fire-damp, and since it is as true in a mine as 
elsewhere that to be forewarned is to be forearmed, this part of 
our subject must not be passed over. It has been noticed that 
many serious explosions have been preceded by rapid falls of 
the barometer, and it is not hard to imagine how sudden dimi- 
nution of atmospheric pressure might well affect so light and 
easily moved a gas as carburetted hydrogen. Every colliery 
ought therefore to be furnished with a good barometer, and its 
readings constantly noted; and whenever a rapid fall takes 
* Among the latest of these experiments are some made at the Barnsley 
Gas Works. See Mining Journal,” 1867, p. 530. 
