“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.”

“Tell me about that, now!  Do you really think they were being run away with?” asked Jerry in a tense tone, as he tried to picture the alarm that must overwhelm aeronauts under such conditions.

“Didn’t Joe say he was sure he heard some one cry out, ‘Help us’?  Wouldn’t that indicate danger for the balloonists?  I tell you what, boys, this was the most remarkable thing that ever happened to us.  To think that the sand bag, and maybe an anchor, knocked our tent down with a smash, and didn’t kill or seriously injure a single one of us beats the record!  But I’m sorry for those fellows, though.”

“So am I, Frank.  I wish we could do something to help them,” remarked Will.

“Couldn’t we put out right away?  They may fall into the gulf any minute, and be drowned!  Say!  Why not go, Frank?” pursued Jerry.

“Get some clothes on, the first thing, fellows.  We’re not going back to bed again now, anyway.  The dawn is surely coming on, and we could get out on the gulf in a short time, if we concluded to try it.”

They had left their outer garments aboard the motor-boat, so that it was easy enough to find them now.  Hastily they dressed, all the while chattering like a lot of magpies.  But it might have been noticed that every one was in favor of doing something to assist the drifting balloonists, who had apparently gone out to sea in a helpless airship.

Frank was dressed a little before any of the rest.  Something seemed to have come into his mind, for he hurried ashore again, as if bent upon examining the sand bag once more.

“What’s he up to?” asked Bluff, for the daylight was now growing strong enough for them to see to some extent.

“Wants to look at that bean bag of Will’s again, I guess.  Perhaps he thinks we may have a good supper off the contents,” jeered Jerry.

“Now I think he expects to get a clue, somehow.  Perhaps there may be a name sewed on the old bag.  Seems to me, balloonists do that, so the people below may report their passing over, especially when there’s a race on,” remarked Will calmly.