“That’s a good plan!” cried the scientist.  “We’ll try it at once.”

Search revealed that two diving suits were among the stores of the Mermaid.  Jack and Mark wanted to be the ones to don them, but as the suits were rather large, and as the professor thought it would take more strength than the boys had to do the work, it was decided that Andy and Washington should make the attempt to cut the ropes.

The hunter and colored man lost little time in getting into the modern armor.  In the meanwhile Jack, who had been posted as a lookout, reported that there seemed to be some activity among the giants.  They were running here and there, and some seemed to be going off toward the woods, that were not far away.

“Now work quickly,” urged the professor.  “We will be on the watch, and as soon as the last rope is cut we will start the machinery and send the ship up.  We will not wait for you to come back inside, so hold fast as best you can when the Mermaid rises.”

“We will,” answered Andy, just before the big copper helmet was fastened on his head, and Washington nodded to show he understood.

The two who were to attempt the rescue of their comrades were soon on deck.  In the conning tower Jack and the professor kept anxious watch, while Mark, Bill and Tom were at the various machines, ready, at the signal, to start the engines.

The giants had now become so interested in whatever plan they had afoot, that they paid little attention to the ship.  Consequently Washington and Andy, crawling along the deck in their diving suits, did not, at first attract any attention.

In fact they had cut several of the big ropes, and it began to look as if the plan would succeed, particularly as they were partly hidden from view by the upper gas holder.  They were working with feverish haste, sawing away at the big cables with keen knives.

“I guess we’ll beat ’em yet!” cried Jack.

“I hope so,” replied the professor.  “It looks——­”

He stopped short, for at that moment a cry arose from the midst of the giants, and one of them pointed toward the ship.  An instant later the air was darkened with a flight of big oranges, which the queer creatures seemed to favor as missiles.  Probably they found stones too heavy.

“Well, those things can’t hurt ’em much with those heavy suits on,” observed Mr. Henderson.  “There, Washington got one right on the head that time, and it didn’t bother him a bit.”

Jack had seen the fruit strike the big copper helmet and observed that the colored man only moved his head slightly in order to get rid of the orange.

In fact the giants, seeing for themselves that this mode of warfare was not going to answer, since the two men on the ship continued to cut the restraining cables, gave it up.  There was a good deal of shouting among them, and a number ran here and there, seemingly gathering up long poles.