The great difficulty, in a real disaster, arises from what are known as "falls." The roof of the mine is normally supported by timbers, and these the explosion moves, so that in places many tons of the earth of which the roof of the mine consists will fall and block completely the "roads" or tunnels which communicate from the shaft to the places where the men are at work. These, of course, have to be removed or burrowed through before the men imprisoned in the distant workings can be reached. The rescue party do not, of course, wait to clear away the whole of this debris, only just enough to enable them to crawl through or over it, but even then it often represents the waste of precious hours, and the expenditure of great exertions, to get past a "fall." So at intervals "falls" are made in the gallery, in order that men may be practised in dealing with them. [Illustration: _By permission of W. E. Garforth, Esq., Pontefract_ AN ARTIFICIAL COAL MINE These two photographs show the clouds of flame and smoke issuing from the mouth of the "Artificial Coal Mine" during the experiments described in the text] It may be interesting to give a brief statement of the training undergone by the men at the Mansfield Rescue Station. In that case, it should be stated, the gallery is made double, so that men can go one way and return the other back to their starting-point. Having donned their breathing apparatus, they enter the gallery, which, by the way, is filled with smoke and foul gas. Passing along it, they encounter two falls, which they must get over or through; then they have to set twelve timber props as might be necessary to maintain the safety of a damaged road in the mine; all that they do three times over. Then they are required to bring up and lay 250 bricks, a thing which might also be necessary in an actual emergency, after which they have to fix up "brattice cloth" in a part of the gallery. One of the first duties, of course, for a rescue party is to restore the circulation of air in the mine, and brattice cloth is a rough kind of cloth which is put to guide the air currents. That done, they have to take a dummy representing a man of 14 stone, put it on a stretcher, and carry it round the gallery and over the falls. Finally, they restore the timber, bricks and cloth, and their turn of work is done. The total time required for this is two hours, and during the whole of that period they are, of course, breathing not the natural air, but the artificial atmosphere provided for them by the apparatus with which each man is provided. The chief point of this part of the training, as has been remarked already, is to accustom the men to the wearing of the apparatus and to doing work in it. By this means they gain confidence in it, and get to know that it will not fail them in the time of trial.