"Who's loony now?" jeered Jack, as he saw the look of dismay on his brother's face.
But the caps were gone and a thorough search of the room, and the entire house as well, failed to disclose them.
"Well, begorra, one thing is certain sure," declared Mike, "them ere caps didn't walk out 'o here all by their lonesome. Somebody sure swiped 'em."
Just then a loud cry of "Bob, Mike, come out here quick," brought them running down the stairs to the back door, where they found Jack on his hands and knees in the path which led to the woods back of the house.
"Say, did either of you go out here since dinner?"
"No," both replied.
"Well then," continued Jack, "you know we had a hard shower just after dinner and these tracks were surely made since then."
"By Jove, that's so," affirmed Bob, examining the tracks carefully. "And look here, these tracks were made by some one wearing sneakers. Now who wears sneakers round here?"
"Why," replied Jack, "Fred and Will Jenkins most always wear them when they are up here."
"That's so, and I'll bet a fishhook that one of them sneaked in here while we were at the boathouse," said Bob. "You remember, don't you Jack, that you saw one of them at the window of the lab when we were trying them? They must have suspected then that we were up to something, and then the fact that we have been hard at work here ever since would make them feel sure that we were doing something to the Sprite."