It was a good deal later when somewhere out of that mass of silence rose the faint beginnings of a sound that stirred first cautiously about the very foundations of the house, and then, mounting inch by inch, through the hall, up the staircase, along the corridor, reached the floor where the secretary slept so peacefully, and finally entered his room.  Its muffled tide poured most softly over all.  At first only this murmur was audible, as of “footsteps upon wool,” of wind or drifting snow, a mere ghost of sound; but gradually it grew, though still gentle and subdued, until it filled the space from ceiling unto floor, pressing in like water dripping into a cistern with ever-deepening note as its volume increased.  The trembling of air in a big belfry where bells have been a-ringing represents best the effect, only it was a trifle sharper in quality—­keener, more alive.

But, also, there was something more in it—­something gong-like and metallic, yet at the same time oddly and suspiciously human.  It held a temper, too, that somehow woke the “panic sense,” as does the hurried note of a drum—­some quick emotional timbre that stirs the sleeping outposts of apprehension and alarm.  On the other hand, it was constant, neither rising nor falling, and thus ordinarily, it need not have stirred any emotion at all—­least of all the emotion of consternation.  Yet, there was that in it which struck at the root of security and life.  It was a revolutionary sound.

And as it took possession of the room, covering everything with its garment of vibration, it slipped in also, so to speak, between the crevices of the sleeping, unprotected Spinrobin, coloring his dreams—­his innocent dreams—­with the suggestion of nightmare dread.  Of course, he was too deeply wrapped in slumber to receive the faintest intimation of this waking analysis.  Otherwise he might, perhaps, have recognized the kind of primitive, ancestral dread his remote forefathers knew when the inexplicable horror of a tidal wave or an eclipse of the sun overwhelmed them with the threatened alteration of their entire known universe.

The sleeping figure in that big four-poster moved a little as the tide of sound played upon it, fidgeting this way and that.  The human ball uncoiled, lengthened, straightened out.  The head, half hidden by folds of sheet and pillowcase, emerged.

Spinrobin unfolded, then opened his eyes and stared about him, bewildered, in the darkness.

“Who’s there?  Is that you—­anybody?” he asked in a whisper, the confusion of sleep still about him.

His voice seemed dead and smothered, as though the other sound overwhelmed it.  The same instant, more widely awake, he realized that his bedroom was humming.

“What’s that?  What’s the matter?” he whispered again, wondering uneasily at the noise.