ONE of the most instructive documents ever penned on the subject of the cause of explosions in collieries has recently appeared, in a lately-issued Blue-book, in the form of a Report to the Home Secretary by Prof. Abel, C.B., F.R.S., of Woolwich, who, at the request of the Home Department, conducted a series of experimental researches upon the cause of the terrible disaster at the Seaham Colliery on September 8, 1880. In 1845 Faraday and Lyell first directed attention to the influence exerted by the presence of coal-dust in mines upon the magnitude of an explosion of fire-damp. In 1867 and 1875, the subject was further advanced in France by Messieurs Verpilleux and Vital, the latter of whom showed that air charged with fine coal-dust, rich in inflammable material, may explode when there is present a much smaller proportion of true fire-damp than is of itself sufficient to constitute the atmosphere an explosive one. Still more recently Mr. W. Galloway has conducted a valuable series of investigations and experiments, the results of which have been communicated to the Royal Society in three very important memoirs. In the first of these he showed that a certain mixture of air and coal-dust, not itself inflammable, became so when there was also present a much smaller proportion of fire-damp than any Davy lamp could detect. In the second he showed that the return-air from the ventilating shaft of a mine may actually contain enough fire-damp to become inflammable when coal-dust is diffused into it. In the third he concludes that the influence of the coal-dust must not be considered as merely aggravating and increasing the explosion originating with the presence of fire-damp, but that the presence of the dust must be regarded as the one thing which, if a small explosion takes place anywhere, will accumulate and carry forward the force of the explosion with ever-increasing energy into every empty space in the workings, however ramified.