In the working of quarries and mines of various kinds, and also in large engineering undertakings, blasting plays a prominent part. Under all conditions blasting is a more or less dangerous business, and it has been the cause of very many serious accidents to the men engaged in carrying it out. Many of these accidents are due to the carelessness resulting from long familiarity with the work, but apart from this the danger lies principally in uncertainty in exploding the charge. Sometimes the explosion occurs sooner than expected, so that the men have not time to get away to a safe distance. Still more deadly is the delayed explosion. After making the necessary arrangements the men retire out of danger, and await the explosion. This does not take place at the expected time, and after waiting a little longer the men conclude that the ignition has failed, and return to put matters right. Then the explosion takes place, and the men are killed instantly or at least seriously injured. Although it is impossible to avoid altogether dangers of this nature, the risk can be reduced to the minimum by igniting the explosives by electricity. Electrical shot firing may be carried out in different ways, according to circumstances. The current is supplied either by a dynamo or by a battery, and the firing is controlled from a switchboard placed at a safe distance from the point at which the charge is to be exploded, the connexions being made by long insulated wires. The actual ignition is effected by a hot spark, as in automobile ignition, or by an electric detonator or fuse. Explosives such as dynamite cannot be fired by simple ignition, but require to be detonated. This is effected by a detonator consisting of a small cup-shaped tube, made of ebonite or other similar material. The wires conveying the current project into this tube, and are connected by a short piece of very fine wire having a high resistance. Round this wire is packed a small quantity of gun-cotton, and beyond, in a sort of continuation of the tube, is placed an extremely explosive substance called “fulminate of mercury,” the whole arrangement being surrounded by the dynamite to be fired. When all is ready the man at the switchboard manipulates a switch, and the current passes to the detonator and forces its way through the resistance of the thin connecting wire. This wire becomes sufficiently hot to ignite the gun-cotton, and so explode the fulminate of mercury. The explosion is so violent that the dynamite charge is detonated, and the required blasting carried out. Gunpowder and similar explosives do not need to be detonated, and so a simple fuse is used. Electric fuses are much the same as detonators, except that the tube contains gunpowder instead of fulminate of mercury, this powder being ignited through an electrically heated wire in the same way. These electrical methods do away with the uncertainty of the slow-burning fuses formerly