Even if you have an order from a D. A. A. G. named Jones, it is very difficult to explain about it when you don't know whether to speak of him as the D. A. A. G. or as General Jones, and especially when a young and inexperienced shadow is twisting his gun about so that the moonlight plays up and down the very longest bayonet ever issued by a civilized nation. They were not nice sentries, either, like those on the Rock, who stand where you can see them, and who challenge you drowsily, like cabmen, and make the empty streets less lonely than otherwise. They were, on the contrary, fierce and in a terrible hurry, and had a way of jumping out of the shadow with a rattle of the gun and a shout that brought nerve-storms in successive shocks. To make it worse, I had gone over the post, while waiting for word from the D. A. A. G., to hear the sentries recite their instructions to the entertaining officer. They did this rather badly, I thought, the only portion of the rules, indeed, which they seemed to have by heart being those which bade them not to allow cows to trespass "without a permit," which must have impressed them by its humor, and the fact that when approached within fifty yards they were "to fire low." I found when challenged that night that this was the only part of their instructions that I also could remember. This was the only trying experience of my stay in Gibraltar, and it is brought in here as a compliment to the force that guards the North Front. For of them, and the rest of the inhabitants and officers of the garrison, any one who visits there can only think well; and I hope when the Rock is attacked, as it never will be, that they will all cover themselves with glory. It never will be attacked, for the reason that the American people are the only people clever enough to invent a way of taking it, and they are far too clever to attempt an impossible thing. II TANGIER A great many thousand years ago Hercules built the mountain of Abyla and its twin mountain which we call Gibraltar. It was supposed to mark the limits of the unknown world, and it would seem from casual inspection, as I suggested in the last chapter, that it serves the same purpose to this day. Men have crept into Africa and crept out again, like flies over a ceiling, and they have gained much renown at Africa's expense for having done so. They have built little towns along its coasts, and run little rocking, bumping railroads into its forests, and dragged launches over its cataracts, and partitioned it off among emperors and powers and trading companies, without having ventured into the countries they pretend to have subdued. But from Paul du Chaillu to W. A. Chanler, "the Last Explorer," as he has been called, just how much more do we know of Africa than did the Romans whose bridges still stand in Tangier?