And now observe the beautiful result of that simple arrangement. Suppose the mine breaks its rope and gets loose, so that it can drift about and carry danger far and wide. It can break loose and it can drift about, but at the very moment of getting loose the danger vanishes, for the rope ceases to pull and the firing mechanism loses its motive power. In other mines the same result has been sought by means of clockwork, which throws the firing arrangements out of action after the lapse of a given time. This scheme of Captain Elia's, however, whereby the very act of breaking adrift produces its own safeguard, is one of the most delightful instances of a happy invention. In conclusion, just a word about the measures taken against mines. Counter-mining is one. It consists in letting off other mines in the midst of a mine-field with the purpose of giving them such a shaking up that some of them will be exploded by the shock. The simplest and indeed the only effective way, however, seems to be the simple primitive method of dragging a rope along between two light draught vessels and thus tearing the mines up by their roots, so to speak. The very act of thus dragging it along by its anchor rope often causes a mine to explode, well astern of the mine-sweeping vessels, but sometimes they are pulled up and fired or sunk by a shot from a gun which the sweeper carries for the purpose. The sweeping up of the mine-fields is a duty often allotted to the steam fishing boats or trawlers, whose crews seem particularly well fitted for the work. It is a hazardous duty, and many lives have been lost through it. Let us hope that in time to come all submarine mines and the dangers connected with them will be a thing of the past, for they are mean, cowardly and contemptible weapons. CHAPTER VI MILITARY BRIDGES Bridging has always been an important part of actual warfare. In my school days I studied "Cæsar" from a textbook which is not much in use nowadays and which had very copious notes, prominent among which was a description, with drawings, of a bridge made by the Roman Legions in Gaul. And a fine bridge it was, too. How its details came to be known was partly through the description given by Cæsar himself and partly by a study of certain old timbers found in the bed of the Rhone, which timbers were believed to be relics of the very bridge which the great Julius himself had had built. This bridge of nearly two thousand years ago appeared to be built of baulks of timber fastened together in very much the same manner as that adopted by the engineering units of the great armies of to-day. Every observant person has noticed how tall poles and short sticks tied together with ropes can be fashioned into the firm, strong scaffolding from which workmen can in safety raise great tall buildings. That mode of construction can always be used to form a bridge.