"Down deep," advised Captain Weston, as he stood beside Tom and Mr. Swift in the pilot house. "As far as you can manage her, and then forward. We'll take no more chances with these fellows."  
"The only trouble is," replied the young inventor, "that the deeper we go the slower we have to travel. The water is so dense¹ that it holds us back."
 
"Well, there is no special need of hurrying now," went on the sailor. "No one is following you, and two or three days difference in reaching the wreck² will not amount to anything."
 
"Unless they repair their rudder, and take after us again," suggested Mr. Swift.
 
"They're not very likely to do that," was the captain's opinion. "It was more by luck than good management that they picked us up before. Now, having to delay, as they will, to repair their steering³ gear, while we can go as deep as we please and speed ahead, it is practically impossible for them to catch up to us. No, I think we have nothing to fear from them."
 
But though danger from Berg and his crowd was somewhat remote, perils⁴ of another sort were hovering⁵ around the treasure-seekers, and they were soon to experience them.
 
It was much different from sailing along in the airship, Tom thought, for there was no blue sky and fleecy clouds to see, and they could not look down and observe, far below them, cities and villages. Nor could they breathe the bracing⁶ atmosphere of the upper regions.
 
But if there was lack of the rarefied air of the clouds, there was no lack of fresh atmosphere. The big tanks carried a large supply, and whenever more was needed the oxygen machine would supply it.
 
As there was no need, however, of remaining under water for any great stretch of time, it was their practice to rise every day and renew the air supply, also to float along on the surface for a while, or speed along, with only the conning⁸ tower out, in order to afford a view, and to enable Captain Weston to take observations. But care was always exercised to make sure no ships were in sight when emerging on the surface, for the gold-seekers did not want to be hailed and questioned by inquisitive⁹ persons.
 
It was about four days after the disabling of the rival submarine, and the Advance was speeding along about a mile and a half under water. Tom was in the pilot house with Captain Weston, Mr. Damon was at his favorite pastime of looking out of the glass side windows into the ocean and its wonders, and Mr. Swift and the balloonist were, as usual, in the engine-room.
 
"How near do you calculate we are to the sunken wreck?" asked Tom of his companion.
 
"Well, at the calculation we made yesterday, we are within about a thousand miles of it now. We ought to reach it in about four more days, if we don't have any accidents."
 
"And how deep do you think it is?" went on the lad.
 
"Well, I'm afraid it's pretty close to two miles, if not more. It's quite a depth, and of course impossible for ordinary divers¹⁰ to reach. But it will be possible in this submarine and in the strong diving suits your father has invented for us to get to it. Yes, I don't anticipate much trouble in getting out the gold, once we reach the wreck of course—"
 
The captain's remark was not finished. From the engine-room there came a startled shout:
 
"Tom! Tom! Your father is hurt! Come here, quick!"
 
"Take the wheel!" cried the lad to the captain. "I must go to my father." It was Mr. Sharp's voice he had heard.
 
Racing⁷ to the engine-room, Tom saw his parent doubled up over a dynamo, while to one side, his hand on a copper¹¹ switch, stood Mr. Sharp.
 
"What's the matter?" shouted the lad.
 
"He's held there by a current of electricity," replied the balloonist. "The wires are crossed."
 
"Why don't you shut off the current?" demanded the youth, as he prepared to pull his parent from the whirring machine. Then he hesitated, for he feared he, too, would be glued fast by the terrible current, and so be unable to help Mr. Swift.
 
"I'm held fast here, too," replied the balloonist. "I started to cut out the current at this switch, but there's a short circuit somewhere, and I can't let go, either. Quick, shut off all power at the main switchboard forward."
 
Tom realized that this was the only thing to do. He ran forward and with a yank cut out all the electric wires. With a sigh of relief Mr. Sharp pulled his hands from the copper where he had been held fast as if by some powerful magnet, his muscles cramped¹² by the current. Fortunately the electricity was of low voltage, and he was not burned. The body of Mr. Swift toppled backward from the dynamo, as Tom sprang to reach his father.
 
"He's dead!" he cried, as he saw the pale face and the closed eyes.
 
"No, only badly shocked, I hope," spoke¹³ Mr. Sharp. "But we must get him to the fresh air at once. Start the tank pumps. We'll rise to the surface."
 
The youth needed no second bidding. Once more turning on the electric current, he set the powerful pumps in motion and the submarine began to rise. Then, aided by Captain Weston and Mr. Damon, the young inventor carried his father to a couch in the main cabin. Mr. Sharp took charge of the machinery¹⁴.
 
Restoratives were applied¹⁵, and there was a flutter of the eyelids¹⁶ of the aged¹⁷ inventor.
 
"I think he'll come around all right," said the sailor kindly¹⁸, as he saw Tom's grief. "Fresh air will be the thing for him. We'll be on the surface in a minute."
 
Up shot the Advance, while Mr. Sharp stood ready to open the conning tower as soon as it should be out of water. Mr. Swift seemed to be rapidly reviving. With a bound the submarine, forced upward from............