the voice of the mate echoed through the mermaid. those on deck heard it, as did tony in the engine room, where he was vainly trying to understand the complicated machinery.

an instant later there sounded from beneath the ship a series of splashes. more sailors were leaping from the deck of the craft to the ocean. the distance was not great, particularly as they all landed in water.

“quick!” cried the mate to a group of sailors that hesitated before taking the jump. “the ship may blow up any minute now.”

the men needed no second urging. as soon as they struck the water they began to swim ashore, as it was not far away. one after another they jumped over the rail. tony was the last to go. he urged the captives to follow him, but they all refused.

a minute later the only one of the pirate crew left on the ship was the mate. the others were all struggling in the sea. eventually they all reached shore in safety.

the airship was now within about twenty feet of the water. it was still falling but not so rapidly.

“better send her up, now,” said the mate to mark, and the boy turned the necessary levers to accomplish this.

dipping into the water as a sea gull does when searching for food on the wing, for she had come quite low, the mermaid mounted once more into the air, and was soon sailing along over the heads of tony and his gang.

“what’s it all about?” asked mr. henderson, who seemed in a sort of stupor. “i thought the ship was broken. how, then, can it rise?”

“it was only a trick of mine,” rodgers said. “the gas machine is not broken. i had mark fix it so that only a little vapor would be generated. when the supply in the holder was not enough, and no more was being made, the ship had to sink. mark and i pretended it was worse than it really was just to scare the scoundrels.”

“and you evidently succeeded,” observed mr. henderson. “they have all left us. i am glad you stayed.”

“so am i,” said rodgers. “i was just waiting for a chance to escape from that crowd. this was the plan i thought of that night. i wanted to see the men put on some island where they could manage to live, and which was not too far away.”

the mermaid was now mounting upward rapidly, as mark had adjusted the machinery properly. the craft was well rid of the pirate crew, and was able to proceed on its way, and enable mr. henderson to carry out his plans.

when the mermaid had reached a certain height her prow was turned the other way, and she was sent back racing over the ground she had just covered. but now the ship was in the hands of friends. fortunately no great damage had been done by the sailors, and the professor was soon able to get things in ship-shape. the engines had not been molested and were working better than ever.

“now to make another attempt to reach the big hole in the earth,” the professor cried. “we will be careful next time, who we rescue from ships at sea.”

the island was soon left behind, becoming a mere speck on the ocean. those aboard the mermaid knew no harm could befall the sailors, as there were no savage tribes on the little spot of land. eventually the sailors were picked up by a passing vessel and taken to their homes. the story of their first mutiny leaked out and they were properly punished.

it required several days travel before the airship regained the distance she had lost because of the plans of the pirates. also, there were a number of minor repairs to make, and the professor and his friends were kept busy.

“how much longer before we come to the big hole?” asked jack, one day.

“i think we ought to be near it in about two weeks,” the professor replied. “i only hope we shall not be disappointed, and will be able to explore it.”

“'tain’t goin’ t’ be no fun t’ be decimated an’ expurgitated inter a conglomerous aggregation of elements constituting th’ exterior portion of human anatomy,” said washington in dubious tones.

“you mean you’re afraid of being boiled in the steam from the big hole?” asked mark.

“jest so,” replied the colored man.

“you don’t need to worry about that,” put in the professor. “i will not take the ship down if there is any danger, though of course there will be some risk.”

the ship, having been fully repaired, was now able to be speeded up, and was sent scudding along toward her destination. rodgers proved a valuable acquisition toward the crew, for he had sailed many years in the waters over which they were flying, and was able to give the professor many valuable hints. he had heard vague stories of the island with the big hole, but had never been near it. he did not make the trip however, as, at his request, he was put off at an inhabited island one night.

it was about a week after the sailors were frightened from the ship, that a curious experience befell mark. washington was on duty in the conning tower, attending to the apparatus as the ship flew through the air, and all the others had gone to bed. mark had remained up, later than the others as he was interested in reading a book on science.

about ten o’clock he became hungry, and going to the pantry got some bread and cold meat. he set these on a table, and then, remembering he would need some water to drink, started after some in the cooler, which was in a little room near the tower.

washington heard the boy as he turned the faucet to draw the liquid, and spoke to him, as the colored man was rather lonesome at his post. mark did not linger more than a minute or two, but when he returned to where he had left the food he was much surprised.

there was not a trace of it to be seen. the dishes were on the table, but every vestige of bread and meat had disappeared.

“i wonder if a cat or dog has been here,” was mark’s first thought. then he remembered that no such animals were aboard the mermaid.

something on the floor caught his eye. he stooped and picked it up. it was a slice of bread, but in such shape that the boy stared at it, puzzled as to how it could have become so.

it was flattened out quite thin, but the strangest part of it was that it bore what seemed to be the marks of thumb and fingers from a very large hand. so big, in fact, was the print, that mark’s hand scarce covered half of it, and, where the bread had been squeezed into a putty like mass (for it was quite fresh) the peculiar markings on the skin of the tips of the fingers were visible.

“it looks as if a giant grabbed this slice of bread,” mark observed. “there are strange happenings aboard this ship. i wish i knew what they meant.”

he looked all around for the food, thinking perhaps a rat had dragged it off, but there was no trace of it.

suddenly the boy thought he heard a sound from the big storeroom. he was almost sure he heard something moving in there. he started toward the door when he was stopped by hearing the professor’s voice call:

“don’t open that door, mark. have i not told you that place must not be entered?”

“i thought i heard some one in there,” mark replied.

“there is nothing in there but some apparatus of mine,” mr. henderson said. “i want no one to see it. what is the matter?”

mark explained matters to the scientist, who had, as he said later, arisen on hearing the boy moving about.

“oh, it was a rat that took your stuff,” mr. henderson said. “i guess there are some pretty big ones on the ship. get some more food and go to sleep.”

mark felt it best to obey, though he was by no means satisfied with the professor’s explanation. he listened intently to see if any more noises came from the storeroom, but none did, and he went to bed.

several times after that mark tried the experiment of leaving food about. on each occasion it was taken.

“it looks as if the ship was haunted,” he said. “of course i know it isn’t, but it’s very queer. they must be strange rats that can get food from shelves when there is only the smooth side of the ship to climb up,” for on some occasions mark had tried the experiment of putting the food as nearly out of reach as possible.

it took several nights to learn all this, and, as he did not want to take any one into his confidence, he had to work in secret. but, with all his efforts he learned nothing, save that there was something odd about the ship that he could not fathom.

at first he believed the professor had some strange animal concealed in the storeroom, but he dismissed this idea almost as soon as he thought of it. for what could the scientist want with an animal when they were going to the interior of the earth? that some beast had slipped aboard was out of the question. mark was much puzzled, but finally, deciding the matter did not concern him a great deal, gave up trying to solve the mystery, at least for a time.

the ship was now in the neighborhood of the equator and the climate had become much warmer. so hot indeed were some nights that they slept out on deck, with the mermaid flying through the air at a moderate pace, for it was deemed best not to go at any great speed after dark.

one night the professor, after consulting various charts and maps, and making calculations which covered several sheets of paper announced:

“we should sight the mysterious island to-morrow.”

“that’s good news!” exclaimed jack. “i’m anxious to see what’s below inside of that big hole.”

“everybody git ready for their funerals!” exclaimed washington in a deep voice. “i ain’t got many——”

“cheer up,” interrupted jack, poking washington in the ribs. the colored man was very ticklish, and he began to laugh heartily, though, perhaps, he did not feel like it.

suddenly, above the sound of his shouts, there came a crashing, grinding noise from the engine room.