Harry made no answer. This waiting in the silence and the night made his blood quiver just a little. He was about to turn back when he saw a sudden flash of fire from another point further up. It was followed by a heavy crash that echoed and re-echoed over the still sea and city. Harry's heart leaped, but his body stiffened to attention. Tom and St. Clair by his side pressed against the earthwork. "What is it?" they whispered. "The moonlight is good," replied Harry, "but I don't see any ship. It must be a signal of some kind." "Hush!" said Langdon, "there it goes again!" Another cannon thundered, and the echoes, as before, came back from sea and shore, followed, as the echoes died, by that strange, heavy silence. But, straining their eyes to the utmost, the three boys could see nothing on the sea. It swayed gently like a vast mass of molten silver in the starshine, and lapped softly against the shore. The report of a third heavy gun came, and then the reports of several more. After that the silence was complete. It had seemed to Harry, his brain surcharged with excitement, like the tolling of great bells. Langdon and St. Clair whispered together, but he said nothing. It was permitted to the three to lie down in their blankets in the earthwork and sleep, but they did not think of trying it. They wished to know the meaning of those cannon shots and they waited, tense with excitement. It was nearly midnight when Colonel Leonidas Talbot came. "We have learned that the Northern vessels will appear before Charleston tomorrow," he said, "and the shots were a signal to all our people to be ready. The attack on Sumter will begin in the morning. Now you three boys must go to sleep. We shall need tomorrow soldiers who are fresh and strong, not those who are worn and weak from loss of sleep." They tried it and found it easier now because they knew the mystery of the shots. Harry became conscious that the night was crisp and cold, and, wrapped in his blanket, he lay with his back against an inner wall of the earthwork. The blood, the result of his tension and excitement, pounded in his ears for some time, but, at last, his pulses became quiet, and his heavy eyes closed. He was awakened at the first shoot of dawn by Colonel Leonidas Talbot. "Up, boys!" he said, "snatch a bite of food and a drink of coffee, and make yourselves as neat as possible. General Beauregard is coming to this very battery." His voice was quick and sharp, and the boys obeyed with the lightning speed of youth. It was a pale dawn. Gray clouds drifted along the sea's far rim, and a sharp wind came out of the Northwest. Heavy waves rolled into the mouths of the narrow and difficult passes that led into the bay. "The Lord Himself fights for us," Harry heard Colonel Leonidas Talbot murmur. "No ships on such a sea would dare the passes in the face of our guns."