"A bean bag! Tell me about that, will you?" said Jerry. And then, as he bent over to clutch hold of it, he went on: "Why, as sure as you live, it's a sand bag! Who ever could have shied that thing at us and then run away?"
Frank was more than startled. He had seen just such bags before, and filled with sand, too. He knew to what uses they were put.
"Say! What do you think, that bag is ballast from a balloon or airship?" he cried.
"Ballast!"
"From an airship!"
The four outdoor chums stood there and stared, first at each other and then at the suspicious bag that lay there on the canvas. There could be no mistake about its contents, for one seam had broken, and the sand was trickling out even now.
"Then a balloon passed over us in the night, and they threw out a sand bag to lighten her! What do you think of that?" gasped Jerry, as if hardly able to grasp the strangeness of the affair.
"Why would they want to lighten her?" asked Bluff.
Frank was quick to perceive facts.
"Listen, fellows! Joe, here, says the voices were out yonder, toward the key, and that they gradually grew less distinct. That would happen, you know, if a balloon were gradually drifting out toward the open gulf."