The extent to which all manufacture and transport, all industry there, was paralyzed during the strike, shows the complete dependence of modern life upon fuel. In spite of the fact that in Great Britain nearly 240,000,000 tons of coal are raised annually, a temporary stoppage of supply threw all the ordinary machinery of existence out of action and revealed the magnitude of the debt that the world owes to those who win precious stores of fuel from the depths of the earth. Probably no industrial operation excites more widespread interest, when accorded publicity, than the mining of coal, and that because of the dangers which attend it. The annual list of victims buried beneath a falling roof, or mangled by runaway cars, causes little comment, but every now and then the world is startled by an appalling catastrophe in which hundreds of men lose their lives. From the early days when growing industry demanded more coal, inventors have been busy devising all sorts of safety appliances for the miner. The original safety-lamp, with which practically everyone is familiar, is the parent of scores of others, each claiming to offer some special advantage. All sorts of mechanical devices to prevent overwinding--an accident which would fling the cage with its coal or human freight out of the pit mouth--have been invented, and every section of the work has been made as safe as human ingenuity and human skill have been able to make it. But the number of disastrous explosions has not been materially reduced. Many varieties of coal give off a gas known as marsh-gas or fire-damp. This is inflammable and, when mixed with air, violently explosive. It is the presence of this gas that necessitates the safety-lamp. There are a few kinds of mines which evolve no gas, and in these naked lights are used. But all mines must be ventilated by forcing air through them with a fan, and this air must be in sufficient quantity to keep the percentage of gas below a dangerous standard. Most mines are examined at regular intervals by a “fireman” who can estimate approximately the percentage of gas present by the size of the faintly luminous “cap” which hovers above the flame of his lamp. Explosions have occurred, however, in cases where it is extremely doubtful whether gas has been present in dangerous quantity, and attention has been drawn to the possible causes. Many varieties of coal produce a quantity of fine dust which settles in the roadways, on roof, and sides, and floor. For many years there has been a controversy as to the relative importance of gas and dust in producing explosions, and the question is still one which gives rise to a lively difference of opinion. But there is no doubt that a mixture of coal-dust and air is explosive, and that even if an explosion is started by gas the disturbance creates clouds of dust which gives rise to secondary explosions and spread the disaster over a wider field than was originally affected.