The little gallery in which we are now stumbling our way over blocks of stone and rubbish, only varied by long tracts of thick slush and pools of water, is the section excavated by the boring-machine--in dimension about twelve feet broad by eight feet high. The tramway which has accompanied us all the way is still continued along this small section. In the middle portion underneath the rails is the canal, inclined toward the mouth of the tunnel, for carrying off the water; and in this canal are now collected the pipes for conveying the compressed air to the machines, and the gas for illuminating the gallery. At the end of a few minutes, a rattling, jingling sound indicates that we are near the end of our excursion, and that we are approaching the perforating-machines. On arriving, we find that nearly the whole of the little gallery is taken up by the engine, the frame of which, mounted upon wheels, rests upon the main tramway, so that the whole can be moved backward or forward as necessary. On examining the arrangement a little closely, we find that in reality we have before us nine or ten perforators, completely independent of one another, all mounted on one frame, and each capable of movement in any direction. Attached to every one of them are two flexible tubes, one for conveying the compressed air, and the other the water which is injected at every blow or stroke of the tool into the hole, for the purpose of clearing out the debris and for cooling the point of the "jumper." In front, directed against the rock, are nine or ten tubes (according to the number of perforators), very similar in appearance to large gun-barrels, out of which are discharged with great rapidity an equal number of boring-bars or jumpers. Motion is given to these jumpers by the direct admission of a blast of compressed air behind them, the return stroke being effected by a somewhat slighter pressure of air than was used to drive them forward. We will suppose the machine brought up for the commencement of an attack. The points most convenient for the boring of the holes having been selected, the nine or ten perforators, as the case may be, are carefully adjusted in front of them. The compressed air is then admitted, and the boring of the holes commences. On an average, at the end of about three-quarters of an hour, the nine or ten holes are pierced to a depth of two feet to two feet six inches. Another ten holes are then commenced, and so on, until about eighty holes are pierced. The greater number of these holes are driven toward the centre of the point of attack, and the rest round the perimeter. The driving of these eighty holes to an average depth of two feet three inches, is usually completed in about seven hours, and the second operation is then commenced.