“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.

“My good friend,” I said, somewhat ironically, I fear, “I am not disposed to question your right to harbor as many spooks as you find agreeable to your taste and consistent with your notions of companionship; that is no business of mine.  But being just a plain man of affairs, mostly of this world, I find spooks needless to my peace and comfort.  I am going to my hotel, where my fellow-guests are still in the flesh.”

It was not a very civil speech, but he manifested no feeling about it.  “Kindly remain,” he said.  “I am grateful for your presence here.  What you have heard to-night I believe myself to have heard twice before.  Now I know it was no illusion.  That is much to me—­ more than you know.  Have a fresh cigar and a good stock of patience while I tell you the story.”

The rain was now falling more steadily, with a low, monotonous susurration, interrupted at long intervals by the sudden slashing of the boughs of the trees as the wind rose and failed.  The night was well advanced, but both sympathy and curiosity held me a willing listener to my friend’s monologue, which I did not interrupt by a single word from beginning to end.

“Ten years ago,” he said, “I occupied a ground-floor apartment in one of a row of houses, all alike, away at the other end of the town, on what we call Rincon Hill.  This had been the best quarter of San Francisco, but had fallen into neglect and decay, partly because the primitive character of its domestic architecture no longer suited the maturing tastes of our wealthy citizens, partly because certain public improvements had made a wreck of it.  The row of dwellings in one of which I lived stood a little way back from the street, each having a miniature garden, separated from its neighbors by low iron fences and bisected with mathematical precision by a box-bordered gravel walk from gate to door.