After he had mounted a dozen steps or so, he paused to take breath. Each step was increasingly difficult to ascend; he felt as though he were carrying a heavy man on his shoulders. It struck a familiar chord in his mind. He went on and, ten stairs higher up, came to a window set in a high embrasure. On to this he clambered, and looked through. The window was of a sort of glass, but he could see nothing. Coming to him, however, from the world outside, a disturbance of the atmosphere struck his senses, causing his blood to run cold. At one moment it resembled a low, mocking, vulgar laugh, travelling from the ends of the earth; at the next it was like a rhythmical vibration of the air—the silent, continuous throbbing of some mighty engine. The two sensations were identical, yet different. They seemed to be related in the same manner as soul and body. After feeling them for a long time, Nightspore got down from the embrasure, and continued his ascent, having meanwhile grown very serious. The climbing became still more laborious, and he was forced to stop at every third or fourth step, to rest his muscles and regain breath. When he had mounted another twenty stairs in this way, he came to a second window. Again he saw nothing. The laughing disturbance of the air, too, had ceased; but the atmospheric throb was now twice as distinct as before, and its rhythm had become _double_. There were two separate pulses; one was in the time of a march, the other in the time of a waltz. The first was bitter and petrifying to feel, but the second was gay, enervating, and horrible. Nightspore spent little time at that window, for he felt that he was on the eve of a great discovery, and that something far more important awaited him higher up. He proceeded aloft. The ascent grew more and more exhausting, so much so that he had frequently to sit down, utterly crushed by his own dead weight. Still, he got to the third window.