Estelle had said the birds he had seen at sunset were pigeons. Perhaps this was one of the great flocks. If it were really so, the food problem would be much lessened, provided a way could be found to secure them. The ammunition in the tower was very limited, and a shell could not be found for every bird that was needed, nor even for every three or four. Great traps must be devised, or bird-lime might possibly be produced. Arthur made a mental note to ask Estelle if she knew anything of bird-lime. A vague, humming roar, altering in pitch, came to his ears. He listened for some time before he identified it as the sound of the wind playing upon the irregular surfaces of the tower. In the city the sound was drowned by the multitude of other noises, but here Arthur could hear it plainly. He listened a moment, and became surprised at the number of night noises he could hear. In New York he had closed his ears to incidental sounds from sheer self-protection. Somewhere he heard the ripple of a little spring. As the idea of a spring came into his mind, he remembered Estelle's description of the deep-toned roar she had heard. He put his hand on the cold stone of the building. There was still a vibrant quivering of the rock. It was weaker than before, but was still noticeable. He drew back from the rock and looked up into the sky. It seemed to blaze with stars, far more stars than Arthur had ever seen in the city, and more than he had dreamed existed. As he looked, however, a cloud seemed to film a portion of the heavens. The stars still showed through it, but they twinkled in a peculiar fashion that Arthur could not understand. He watched in growing perplexity. The cloud moved very swiftly. Thin as it seemed to be, it should have been silvery from the moonlight, but the sky was noticeably darker where it moved. It advanced toward the tower and seemed to obscure the upper portion. A confused motion became visible among its parts. Wisps of it whirled away from the brilliantly lighted tower, and then returned swiftly toward it. Arthur heard a faint tinkle, then a musical scraping, which became louder. A faint scream sounded, then another. The tinkle developed into the sound made by breaking glass, and the scraping sound became that of the broken fragments as they rubbed against the sides of the tower in their fall. The scream came again. It was the frightened cry of a woman. A soft body struck the earth not ten feet from where Arthur stood, then another, and another. XI. Arthur urged the elevator boy to greater speed. They were speeding up the shaft as rapidly as possible, but it was not fast enough. When they at last reached the height at which the excitement seemed to be centered, the car was stopped with a jerk and Arthur dashed down the hall. Half a dozen frightened stenographers stood there, huddled together. "What's the matter?" Arthur demanded. Men were running, from the other floors to see what the trouble was.