"I wonder what or who that was," reasoned Mark. "There is some mystery in this. Can the professor have concealed some one on this ship whose presence he does not want to admit? It certainly looks so."

Not wanting to awaken the ship's crew, and remembering what Mr.

Henderson had said about any one entering the storeroom, Mark went back to bed, to fall into an uneasy slumber.

"Breakfast!" called Washington breaking in on a fine dream Jack was having about being captain of a company of automobile soldiers. "Last call for breakfast!"

"h.e.l.lo! Is it morning?" asked Jack.

"Not so's you could notice it," Washington went on. "It's as dark as a stack of black cats and another one throwed in. But breakfast is ready jest the same."

The boys were soon at the table, and learned that nothing of importance had occurred during the night. The Mermaid had been kept going slowly down, and about seven o'clock registered more than fifty miles below the earth's surface.

Still there was no change in the outward surroundings. It remained as black as the interior of Egypt when that country was at its darkest.

The powerful electrics could not pierce the gloom. The ship was working well, and the travelers were very comfortable.

Down, down, down, went the Mermaid. The temperature, which had risen to about ninety went back to sixty-nine, and there seemed to be no more danger from the inner fires.

They were now a hundred miles under the surface. But still the professor kept the Mermaid sinking. Every now and again he would take an observation, but only found the impenetrable darkness surrounded them.

"We must arrive somewhere, soon," he muttered.

It was about six o'clock that night that the alarm bell set up a sudden ringing. The professor who was making some calculations on a piece of paper jumped to his feet, and so did a number of the others.

"We are nearing the bottom!" he cried. "The bell has given us warning!"

CHAPTER XV

IN THE STRANGE DRAUGHT

THE boys ran to attend to the engines and apparatus to which they had been a.s.signed in view of this emergency. The professor, Washington, Bill, Tom and Andy, who had kept to themselves since the descent, came running out of the small cabin where they usually sat, and wanted to know what it was all about.

"We may hit something, in spite of all precautions," Mr. Henderson remarked. "Slow down the ship."

The Mermaid was, accordingly checked in her downward flight, by a liberal use of the gas and the negative gravity machine.

The bell continued to ring, and the dials pointed to the mark that indicated the ship was more than one hundred and fifty miles down.

Mark, who had run to the engine room to check the descent, came back.

"Why didn't you slow her down?" asked the professor.

"I did," replied the boy. "The negative gravity and the gas machines are working at full speed."

"Then why are we still descending?" asked the scientist. "For a while our speed was checked, but now we are falling faster than before."

"I attended to the apparatus," Mark insisted.

Just then, from without the ship, came a terrible roaring sound, as though there was a great cyclone in progress. At the same time, those aboard the craft could feel themselves being pulled downward with terrific force.

"We are caught in a draught!" Mr. Henderson cried. "We are being sucked down into the depths of the earth!"

He ran to the engine room. With the help of the boys he set in motion an auxiliary gravity machine, designed to exert a most powerful influence against the downward pull of the earth. As they watched the great wheels spin around, and heard the hum and whirr of the dynamos, the boys watched the pointer which indicated how low they were getting.

And, as they watched, they saw that the needle of the dial kept moving, moving, moving.

"Our efforts are useless! We can't stop!" the professor cried.

Grave indeed was the plight of the adventurers. In their ship they were being sucked down into unknown regions and all their efforts did not avail to save them. It was an emergency they could not guard against, and which could not have been foreseen.

"What are to do?" asked Mark.

"We can only wait," Mr. Henderson replied. "The terrible suction may cease, or it may carry us to some place of safety. Let us hope for the best."

Seeing there was no further use in running the engines in an effort to check the downward rush the machines were stopped. Then they waited for whatever might happen.

Now that they seemed in imminent peril Washington was as cool as any one. He went about putting his kitchen in order and getting ready for the next meal as if they were sailing comfortably along on the surface of the ocean. As for old Andy he was nervous and frightened, and plainly showed it. With his gun in readiness he paced back and forth as if on the lookout for strange beasts or birds.

Bill and Tom were so alarmed that they were of little use in doing anything, and they were not disturbed in their staterooms where they went when it became known that the ship was unmanageable.

The boys and the professor, while greatly frightened at the unexpected turn of events, decided there was no use in giving way to foolish alarm. They realized they could do nothing but await developments.

At the same time they took every precaution. They piled all the bedding on the floor of the living room, so that the pillows and mattresses might form a sort of pad in case the ship was dashed down on the bottom of the big hole.

"Not that it would save us much," Jack observed with a grim smile, "but somehow it sort of makes your mind easier."

All this while the ship was being sucked down at a swift pace. The pointer of the gage, indicating the depth, kept moving around and soon they were several hundreds of miles below the surface of the earth.

The professor tried, by means of several instruments, to discover in which direction they were headed, and whether they were going straight down or at an angle. But some strange influence seemed to affect the gages and other pieces of apparatus, for the pointers and hands would swing in all directions, at one time indicating that they were going down, and, again, upward.

"There must be a strong current of electricity here," Mr. Henderson said, "or else there is, as many suspect, a powerful magnet at the center of the earth, which we are nearing."

"What will you do if the ship is pulled apart, or falls and is smashed?" asked Mark with much anxiety.

"You take a cheerful view of things," said Jack.

"Well, it's a good thing to prepare for emergencies," Mark added.

"If the ship was to be separated by the magnetic pull, or if it fell on sharp rocks and was split in twain, I am afraid none of us could do anything to save ourselves," the professor answered. "Still, if we were given a little warning of the disaster, I have means at hand whereby we might escape with our lives. But it would be a perilous way of----"

"I reckon yo' all better come out an' have supper," broke in Washington. "Leastways we'll call it supper, though I don't rightly know whether it's night or mornin'. Anyhow I've got a meal ready."

"I don't suppose any of us feel much like eating," observed Mr.

Henderson, "but there is no telling when we will have the chance again, so, perhaps, we had better take advantage of it."

For a while they ate in silence, finding that they had better appet.i.tes than they at first thought. Old Andy in particular did full justice to the food Washington had prepared.