I found a chance to interject a query. "But how?" I asked. "That's what interests me, the method of traveling through time at will. I've heard theories on that subject, but this actual accomplishment, this power to race into past or future--have you no idea as to how that is done, Cannell?" He considered before answering. "The transformation into a gaseous form when time-traveling is a significant detail," he said. "I have an inkling of what power the Raider utilizes to speed through time. I was in the thing's grip only for a few minutes, but I noticed some things, even in that short time, that set me thinking, afterward. I formed a rough theory concerning the method of time-traveling, and on the voyage home I jotted down some notes concerning it, intending to investigate the matter later." Reaching into an inside pocket, he brought forth a little packet of soiled envelopes and folded sheets. "My own idea about it--" he began, then suddenly broke off speaking and sat motionless, listening tensely. Astonished, we listened likewise, but the only sound was the far dim roar of the city below, and the curtains at the open French windows, billowing gently in a soft breeze. From an adjoining room came the faint chime of a clock. Relief dropped on Cannell's face, and its tense outlines relaxed. "I thought I heard--" he murmured, then abruptly stopped and jumped to his feet, his eyes wild. My heart gave a sudden great throb, for through the open windows came the sound of a high, thin whistling, far and faint and crystal-clear, an eery chorus of piercing knife-blades of sound, that shrilled out louder and louder, swelling to a roaring tumult of wind-sounds. The window-curtains whipped up madly, in a buffeting gale, as through the windows came a breath of icy air. Abruptly the lights of the room went out, plunging us into darkness. There was a shout from Lantin: "The switch!" and I heard him running toward it. Outside the wind-shrieks had risen to a thundering bellow, and there were cries and running feet, somewhere in the building below us. A dark, erect figure appeared in the open window, silhouetted blackly against the brilliant lights of the distant streets. It poised there a moment, then passed out onto the outside roof, walking stiffly and unhumanly, like a puppet pulled by unseen strings. "Cannell!" I cried; "get back!" I raced across the room toward the window, and in the darkness collided with Lantin, who was making for the same objective. We staggered, recovered our balance, rushed together to the window, and then recoiled.