“What’s that, Frank?” demanded Jerry.

“The balloon must have dropped into the water.  If it was still in the air it could be seen through these powerful glasses miles away.”

The others recognized the truth of his words.

“You seem to be heading straight out.  Have you any reason for such a thing?” asked Bluff, seeking information.

“I have.  Before we started I carefully noted my bearings.  I also made sure that what little air was stirring came direct from the land, which, in this case, was almost due east.  You can easily see from that which way the balloon must have drifted up to the minute it dragged in the water.”

“Frank, what you say is sound, practical good sense.  We must come on some sign in a short time, if we keep straight on and the conditions remain the same.  I’m only afraid we may be too late,” remarked Jerry sadly.

No one else spoke for several minutes as the motor-boat sped merrily along on her mission of mercy.  It was a time of great strain.  They hoped for the best, and yet were conscious of a terrible fear lest the professor and his assistant might have gone down long ere this.

“The breeze is freshening,” remarked Bluff presently.

Frank had noted this, too.  It was only natural, for after dawn the air currents that may have become sluggish during the night were in the habit of awakening and taking on new life.

He looked back.  The land was several miles away by this time.  If they were fated to meet with success in their errand, something must be showing up very soon now.

Sick at heart with apprehension, Frank handed the glasses over to Jerry, and was pretending to pay strict attention to the motor.  Truth to tell, his nerves were keyed up to a high tension, as he counted the seconds, and kept hoping for the best.

Frank had noted one thing that gave him not a little concern.  This was in connection with the fact that the easterly breeze seemed to have bobbed around to the southwest.  Now, from all that he had heard this was a quarter that nearly always brings one of those howling “northers” that prove such a bane to Florida cruisers.

“How about that, Joe—­is the fact that the wind is in the southwest apt to bring bad weather?” he asked, when he could get the cracker lad aside; for Frank did not wish to further alarm his chums.

“Most always that happens.  When the wind rises now, unless she goes back once again to the south, you see she will be squally,” returned Joe, also lowering his voice cautiously.

“And that squally wind develops into something stronger, I guess?” pursued the Northern boy, always seeking to learn.

“It jumps around to the northwest like a pompano skipping along the water in a shoal.  Then for three days it blows like a railroad train, out of the north, and we all shiver,” was the characteristic reply.

“Well, I only hope the squall part of it holds off until we pick up the poor professor.  We saved him once from the fire, and now it seems up to us to pull him in out of the wet, if we have any decent sort of luck.”