Then they fell asleep. During the night and the next day the _Porpoise_ forged on underneath the waves. Washington relieved Mr. Henderson in the conning tower and reported the machinery to be working well.

"Keep her headed due south," was the order of the inventor, and the colored man did so.

It was about four o'clock one morning that Washington felt a slight jar to the submarine.

"Hope we ain't goin' to hit no more battleships," he said.

He glanced at the speed-indicating gage. To his surprise it stood at zero. The craft was not moving forward a foot! Yet the engines were going at half speed!

In great alarm Washington shut off the power and ran to acquaint Professor Henderson with the news.

"Suffin's ketched us!" cried the colored man.

"Nonsense!" said the inventor, yet he seemed alarmed as he slipped on his clothes and hastened to the conning tower.

He peered ahead along the path of water illuminated by the glare of the searchlight, but nothing was to be seen. Then he started the engine, increasing the speed gradually until the big screw in the shaft revolved more than one thousand times a minute. Still the _Porpoise_ never stirred. She remained in the same position, as if some giant hand grasped her.

"Reverse the engine," said the professor.

Washington did so. To the surprise of both of them the ship shot backward like a frightened crab.

"Now forward!" exclaimed the old inventor.

But this time the _Porpoise_ did not move. It was as if she was up against a stone wall.

"What's the matter?" asked Mark, who had been awakened by the excitement on board.

"I do not know," replied Mr. Henderson gravely. "Something mysterious has occurred. We can go no further!"

CHAPTER VIII

ASh.o.r.e IN THE DARK

"Stop the engine," the captain commanded after he had peered through the lens in the conning tower for some time. "We must see what is the matter."

He glanced at the depth gage and noted that they were now four hundred feet below the surface. Then he consulted some charts.

"There is a depth of one thousand feet about here," he remarked. "Lower the ship, Washington. Let us see if by getting on the ocean bed we can get away from this obstruction."

The colored man opened wider the sea c.o.c.ks by which the tanks were filled. The increased ballast sunk the _Porpoise_ still lower, and, in a few minutes a slight jar told the navigators that they were on the bottom of the ocean.

"Now we will see if we have cleared the obstruction," said the professor.

He started the big screw to revolving, but the ship did not move. It shivered and trembled throughout its length but remained stationary.

"Maybe dar's a debil fish what hab circ.u.mulated dis ship in de exteror portion ob his anatomy," suggested Washington, rolling his eyes until only the whites were visible.

"I presume you mean that a giant squid or cuttle fish has attacked us,"

spoke the professor.

"Yas, sir," replied Washington.

"That's nonsense," went on the inventor. "However, we must make an investigation."

"How are you going to do it?" asked Mark. "You can't see the end of the tube from inside the ship, and, even if we went to the surface it would still be under water."

"We are going to look at it while here, under the ocean," said the inventor.

"Well, maybe you're a good swimmer," put in Jack, "but I don't believe you can stay under, in this depth of water, long enough to see what the trouble is."

"I think I can," answered Mr. Henderson.

"How?"

"I'll show you. Washington, bring out the diving suits."

The colored man, his eyes growing bigger every minute, went to a locker and brought out what seemed quite a complicated bit of apparatus.

"With the aid of these," said the professor, "I will be able to go out, walk along the ocean bed, and investigate the mystery. Do you boys want to come along?"

"Is it safe?" asked Mark, who was inclined to be cautious.

"As safe as any part of this under-sea voyage," replied the professor.

"These diving suits are something I have not told you about," he went on. "They are my own invention. Besides the regular rubber suits there is an interlining of steel,--something like the ancient suits of chain mail--to withstand the great pressure of water. Then, instead of being dependent on a supply of air, pumped into the helmet from an apparatus in a boat on the surface, each person carries his own air supply with him."

"How is that?" asked Jack, and Mark also asked the question.

"Simply by attaching a little tank of the compressed gas to the shoulder piece of the suit," said the inventor. "There is enough air in the tank to last for nearly a day. It is admitted to the helmet as needed by means of automatic valves. In other respects the diving suit is the same as the ordinary kind, except that there is a small searchlight, fed by a storage battery, on top of the helmet."

In spite of their fears at venturing out under the great ocean, the two boys were anxious to try the suits. So, after some hesitation, they donned them.

"Here, take these with you," said the professor, before their helmets were screwed on. He held out what looked like long sticks.

"What are they?" asked Jack.

"Electric guns," replied the professor. "But come on now, we have no time to lose."

Further conversation was impossible, for the boys had their heavy copper helmets on, and they were as tightly enclosed as if inside a box. They grasped their weapons and waited for the next move.

The professor led the way to the stern of the ship. The boys found it hard to walk, as they were weighted down by the heavy suits, and also the boots, the soles of which were of lead.

They followed the inventor into what seemed a small room. Inside they found themselves in darkness. There was a clanking sound as Washington fastened and clamped the door shut. Then came a hissing.

The boys felt water rising about them. They could experience its coldness, even through the diving suits. They were much afraid, but the professor put a rea.s.suring hand on their shoulders.