"Yes. This is what's been throwing the hammer off the guides all the while," and Tom pulled out a small steel bolt that had been slipped into an oil hole. A certain amount of vibration, he explained to Ned, would rattle the bolt out so that it would force the hammer to one side, throwing it off the channel-plates, and rendering it useless for the time being. "A foxy trick," commented Tom. "No wonder the machine got out of kilter so easily." "Do you think it was done purposely?" "Well, I'm not going to say. But I'm going to watch that man. He wants to be transferred to the airship department. He put this in the hammer, perhaps, to have an excuse for a change. Well, I'll give it to him." "You don't mean that you'd take a fellow like that and put him to work on your new aerial warship, do you, Tom?" "Yes, I think I will, Ned. You see, I look at it this way: I haven't any real proof against him now. He could only laugh at me if I accused him. But you've heard the proverb about giving a calf rope enough and he'll hang himself, haven't you?" "I think I have." "Well, I'm going to give this fellow a little rope. I'll transfer him, as he asks, and I'll keep a close watch on him." "But won't it be risky?" "Perhaps, but no more so than leaving him in here to work mischief. If he is hatching a plot, the sooner it's over with the better I shall like it. I don't like a shot to hang fire. I'm warned now, and I'll be ready for him. I have a line on whom to suspect. This is the first clue," and Tom held up the incriminating bolt. "I think you're taking too big a risk, Tom," his chum said. "Why not discharge the man?" "Because that might only smooth things over for a time. If this plot is being laid the sooner it comes to a head, and breaks, the better. Have it done, short, sharp and quick, is my motto. Yes, I'll shift him in the morning. Oh, but I wish it was all over, and the Mars was accepted by Uncle Sam!" and Tom put his hand to his head with a tired gesture. "Say, old man!" exclaimed Ned, "what you want is a day off, and I'm going to see that you get it. You need a little vacation." "Perhaps I do," assented Tom wearily. "Then you'll have it!" cried Ned. "There's going to be a little picnic to-morrow. Why can't you go with Mary Nestor? She'd like you to take her, I'm sure. Her cousin, Helen Randall, is on from New York, and she wants to go, also." "How do you know?" asked Tom quickly. "Because she said so," laughed Ned. "I was over to the house to call. I have met Helen before, and I suggested that you and I would take the two girls, and have a day off. You'll come, won't you?" "Well, I don't know," spoke Tom slowly. "I ought to--" "Nonsense! Give up work for one day!" urged Ned. "Come along. It'll do you good--get the cobwebs out of your head." "All right, I'll go," assented Tom, after a moment's thought.