THE Spaniards sharing the sick man's tent willingly complied with Charley's request and moved their belongings to the other tents in which there was plenty of room for them. With Walter's assistance the lad cleaned the tent out thoroughly and tied back the flaps at both ends to permit the free circulation of air. Rama was made to go to bed on a second cot and given a dose of the same medicine given the other. This done, Charley called the balance of the graders and ground men together and gave them a large bottle of carbolic acid and a box of salve, instructing them how to use both. It was now getting dark, and after a hasty supper the boys with their two Spaniards repaired to the guard line. Before night, however, Walter had climbed a small tree and taken a survey of the country. Much to his disappointment, he had seen smoke rising from the convicts' old camping place, showing that the gunmen had returned to their old haunts. "I wonder how they manage to find our camp so easy at night," the lad remarked, as he and his chum met on their rounds. "When McCarty and I were out hunting that time we could not see this camp from theirs, and after we camped in the thicket we could not see their camp, although we were not over half a mile away. The white mist blotted out everything." "That digging light way up on the machine's boom guides them," Charley answered. "The mist is densest close to the ground. The further up one goes the thinner it gets; consequently they can see that light even when they can't see our campfire." "Simple enough, after all," Walter commented. "It's the simple things that puzzle one the most sometimes." "Which reminds me of what Mr. Bruce hinted," Charley said, "that the solution of our mystery was in plain sight all the time, but hanged if I haven't puzzled over it till I made my head swim and can't make it out." "Same here," Walter said. "I hope he is right and can make an end to this trouble, but I doubt it." "Well, we will know in a few days. He promised to be out again within a week." The lads turned back on their patrol and the conversation ceased. The hours slipped slowly away while the four guards kept up their slow, weary, monotonous pacing back and forth. Three times Charley slipped in and administered doses of quinine. On the last trip he passed by the cook tent and, striking a match, glanced at the clock inside. "It's just midnight," he said as he rejoined his chum. "That seems to be the favorite time for their devilment. I suppose we can look for trouble any minute now." He had hardly finished when there came the sharp crack of rifles from about the machine. "Good," Charley exclaimed, "they haven't all got silent guns this time. Those reports will give our men an idea where to shoot." "Hadn't we better go out there?" Walter asked. "No, we may have our hands full here," his chum replied. "Besides, the engineer will whistle if he wants us. Gee, look at that!"