“I fancy that it will be long,” I said, “before human speech will cease to serve our need; and then the need, with its possibilities of service, will have passed.” He made no reply, and I too was silent, for the talk had taken a dispiriting turn, yet I knew not how to give it a more agreeable character. Suddenly, in a pause of the storm, when the dead silence was almost startling by contrast with the previous uproar, I heard a gentle tapping, which appeared to come from the wall behind my chair. The sound was such as might have been made by a human hand, not as upon a door by one asking admittance, but rather, I thought, as an agreed signal, an assurance of someone’s presence in an adjoining room; most of us, I fancy, have had more experience of such communications than we should care to relate. I glanced at Dampier. If possibly there was something of amusement in the look he did not observe it. He appeared to have forgotten my presence, and was staring at the wall behind me with an expression in his eyes that I am unable to name, although my memory of it is as vivid to-day as was my sense of it then. The situation was embarrassing; I rose to take my leave. At this he seemed to recover himself. “Please be seated,” he said; “it is nothing—no one is there.” But the tapping was repeated, and with the same gentle, slow insistence as before. “Pardon me,” I said, “it is late. May I call to-morrow?” He smiled—a little mechanically, I thought. “It is very delicate of you,” said he, “but quite needless. Really, this is the only room in the tower, and no one is there. At least—” He left the sentence incomplete, rose, and threw up a window, the only opening in the wall from which the sound seemed to come. “See.” Not clearly knowing what else to do I followed him to the window and looked out. A street-lamp some little distance away gave enough light through the murk of the rain that was again falling in torrents to make it entirely plain that “no one was there.” In truth there was nothing but the sheer blank wall of the tower. Dampier closed the window and signing me to my seat resumed his own. The incident was not in itself particularly mysterious; any one of a dozen explanations was possible (though none has occurred to me), yet it impressed me strangely, the more, perhaps, from my friend’s effort to reassure me, which seemed to dignify it with a certain significance and importance. He had proved that no one was there, but in that fact lay all the interest; and he proffered no explanation. His silence was irritating and made me resentful.