enough for me."

That night Mark and Jack were thinking so much of the proposed test of the ship the next day that they each dreamed they were sailing beneath the waves, and Jack woke Mark up by grabbing him about the neck during a particularly vivid part of the vision.

"What's the matter?" inquired Mark, sleepily.

"I thought the ship turned over and spilled me out and I was drowning," explained Jack. "I grabbed the first thing I got hold of and it happened to be you."

"Well, as long as you're safe you can go to sleep again," said Mark. "I dreamed I was chasing a whale with the Porpoise."

The boys were up early the next morning, and found the professor and Washington before them. The inventor was inspecting the track which had been built from the shed down to the water's edge to enable the Porpoise to slide into the ocean.

With him were the two machinists, Henry Watson and James Penson. They had been busy since daylight making the ways secure.

"She goes in after breakfast," announced the professor, "and I'm going to let you christen her, Washington."

"Me? I neber christened a ship," objected the colored man.

"Nothing like learning," remarked Mr. Henderson.

"Has you got the bottle ob wine?" asked Washington.

"I guess soda water will do," said the inventor. "Now look sharp, boys. Get your breakfasts and we'll see if the ship will come up to our expectations."

No one lingered over the meal. When it was finished the professor gave Washington a few instructions about breaking the bottle over the nose of the Porpoise as she slid down to the water, for there was no bow to such a queerly shaped vessel as the submarine.

At last all was in readiness. The two machinists knocked away the last of the retaining blocks and eased the ship slightly down the well-greased timbers of the ways.

"There she goes!" cried the professor. "Break the bottle, Washington!"

"In de name ob de Stars an' Stripes, in de name of liberty, de home of the free an' de land ob de brave, I names yo' Mrs. Porpoise!" cried the colored man, but he was so long getting the words out, and so slow in swinging the bottle of soda, that the ship was quite beyond his reach when he had finished his oration. He was not to be outdone, however, and, with a quick movement he hurled the bottle at the moving ship. It struck the blunt nose squarely, and shivered to pieces.

"Three cheers for de south pole!" yelled Washington, and the others joined in.

The next instant the Porpoise was riding the waves of the little bay, dancing about as lightly as a cork, though, from the nature of her construction, she was quite low in the water, only about three feet of freeboard showing where the platform was located.

"Well, she floats, anyhow," remarked the professor. "Row out and fasten cables fore and aft," he went on, turning to the two machinists. In a few minutes the Porpoise was fastened to a small dock with strong ropes the two young men had carried out to her in rowboats.

"We will go aboard in a little while," the professor said. "I am anxious to see if she rides on an even keel and how the sinking tanks work."

Aided by the boys, he and Washington carried on board a number of tools and appliances. Then, with the two machinists, they all descended into the interior of the craft through the small manhole in the middle of the deck or platform.

Inside the Porpoise, the greater part of which was below the surface of the waves and consequently in darkness, the professor switched on the electric lights and then he proceeded to get up steam.

The propelling power of the craft has already been described. In order to make the ship sink beneath the water all that was necessary was to incline the rudder and open certain valves in the four tanks, when the water, rushing in, would sink her. There was a tank on either side, and one each fore and aft. If it was desired to sink straight down all four tanks were filled at once. If the professor wanted to descend slanting either to the front or back, only one of the end tanks was filled, according to the direction desired. The deflecting rudder also aided greatly in this movement.

To cause the ship to rise the tanks were emptied of the water by means of powerful pumps. The filling of the tanks, as well as the emptying of them, the starting or stopping of the engine that moved the boat, as well as the control of most of the important machinery on the craft could be accomplished from the conning or steering tower, as well as from the engine-room.

There were numerous gages to tell the depth to which the ship had sunk, the steam pressure, density of the water, and other necessary details.

There were dynamos to make light, motors to run the pumps, and a great storage battery, so that in case of a breakdown to the turbine engine the craft could be run entirely by electricity for a time.

The cooking was all done by this useful current, and all that was necessary to make a cup of coffee or fry a beefsteak was to turn a small switch of the electric stove.

The professor was busy over the machine for generating gas, that furnished the heat to create steam. Soon a hissing told that it was working. In a few minutes the hum and throb of the engine told that it was ready to start.

"We are only going down a little way," the professor said, "and only going to travel a short distance under water for the first time. I think there is no danger, but if any of you want to back out, now is your chance."

No one seemed inclined to withdraw, though Mark said afterward he thought Washington got as pale as it is possible for a colored man to get.

"We will all put on life preservers," the inventor went on, "and one of you will be stationed near the emergency exit. In case anything goes wrong, and I cannot make the ship rise, by pulling the lever the top of the craft will be forced off, and, we can at least save our lives. I think we are all ready now. Mark, you clamp down the manhole cover, and Jack, after you close the conning tower station yourself at the emergency lever after we have donned the life preservers."

The cork jackets were adjusted and Mark clamped the manhole cover on. The professor took one last look at the various levers and handles, and then turned the wheel that admitted water to all four tanks. There was a hissing sound as the sea water rushed in, and the Porpoise gave a sudden lurch.

Then they could all feel the submarine sinking. Down and down she went. Would she ever stop? Would the professor be able to raise her again? There were questions that troubled everyone.

Down and down the craft sunk, until by the gage it was indicated that she was twenty feet below the surface. Then the professor shut off the inrush of water and the Porpoise floated away below the surface of the waves.

There was a clicking sound and all the lights went out. The boys and Washington gave a gasp of terror. What did the sudden blackness mean.

"Open the side windows," called the professor's voice, and the two machinists obeyed. Heavy steel doors that covered plate glass windows in either side of the craft were pulled back, and a cry of astonishment broke from the boys.

They looked out and saw staring in at them, so close it seemed that they could touch them, scores of fishes that looked in through the glass bull's-eyes.

For the first time they realized that they were in the depths of the ocean.