The surface of the river was now dark. The stream flowed gently, and without noise. It, too, struck upon the boy's imagination. It would be fitting for an Indian canoe to come stealing down in the darkness, and he almost fancied he could see it there. But no canoe came, and Ned walked back and forth in a little space, always watching the wood or the river. The night was very quiet. The horses, having grazed for an hour or two, now rested content. The men not on guard, used to taking their sleep where they could find it, were already in slumber. There was no wind. The dark hours as usual were full of chill, but Ned's vigorous walk back and forth kept him warm. He was joined after a while by the famous scout, Henry Karnes, who, like "Deaf" Smith, seemed to watch all the time, although he came and went as he pleased. "Well, boy," said Karnes, "do you find it hard work, this watching and watching and watching for hours and hours?" "Not at all," replied Ned, responding to his tone of humorous kindness. "I might have found it so once, but I don't now. I'm always anxious to see what will happen." "That's a good spirit to have," said Karnes, smiling, "and you need it down here, where a man must always be watching for something. In Texas boys have to be men now." He walked back and forth with Ned, and the lad felt flattered that so famous a scout should show an interest in him. The two were at the edge of the wood and they could see duskily before them a stretch of bare prairie. Karnes was watching this open space intently, and Ned was watching it also. The boy saw nothing, but suddenly he heard, or thought he heard, a low sound. It was faint, but, unconsciously bending forward a little, he heard it again. It was a metallic rattle and instantly he called the attention of Karnes to it. The scout stopped his walk and listened. Then Ned saw his form grow rigid and tense. "Let's put our ears to the ground, Ned," said he. The two stretched out ear to earth, and then Ned not only heard the noise much more distinctly, but he knew at once what it was. He had heard it more than once in the marching army of Cos. It was the sound made by the approaching wheel of a cannon. "Artillery," he said in a whisper. "Beyond a doubt," said Karnes. "It means that the Mexicans have crossed the river--there's a ford two or three hundred yards above--and mean to attack us. It was your good ear, Ned, that gave us the first warning." Ned flushed with pleasure at the compliment, but, a moment or two later, they saw dark figures rising out of the prairie and advancing toward them. "Mexicans!" cried Karnes, and instantly fired at a dusky outline. The figures flitted away in the dusk, but the camp of Bowie was aroused at once. Inside of a minute every man was on his feet, rifle in hand, facing the open place in the horseshoe. They knew that they could not be attacked from the river. Bowie came to the side of Ned and Karnes. "What is it?" he asked.