There was no doubt that the steamer was coming after the submarine. Several observations Captain Weston made confirmed this, and he reported the fact to Mr. Swift.  
"Well, we'll change our plans, then," said the inventor. "Instead of sailing on the surface we'll go below. But first let them get near so they may have the benefit of seeing what we do. Tom, go below, please, and tell Mr. Sharp to get every thing in readiness for a quick descent. We'll slow up a bit now, and let them get nearer to us."
 
The speed of the submarine was reduced, and in a short time the strange steamer had overhauled¹ her, coming to within hailing distance.
 
Mr. Swift signaled for the machinery² to stop and the submarine came to a halt on the surface, bobbing about like a half-submerged bottle. The inventor opened a bull's-eye in the tower, and called to a man on the bridge of the steamer:
 
"What are you following us for?"
 
"Following you?" repeated the man, for the strange vessel³ had also come to a stop. "We're not following you."
 
"It looks like it," replied Mr. Swift. "You'd better give it up."
 
"I guess the waters are free," was the quick retort. "We'll follow you if we like."
 
"Will you? Then come on!" cried the inventor as he quickly closed the heavy glass window and pulled a lever. An instant later the submarine began to sink, and Mr. Swift could not help laughing as, just before the tower went under water, he had a glimpse of the astonished face of the man on the bridge. The latter had evidently not expected such a move as that.
 
Lower and lower in the water went the craft, until it was about two hundred feet below the surface. Then Mr. Swift left the conning⁴ tower, descended⁵ to the main part of the ship, and asked Tom and Captain Weston to take charge of the pilot house.
 
"Send her ahead, Tom," his father said. "That fellow up above is rubbing his eyes yet, wondering where we are, I suppose."
 
Forward shot the Advance under water, the powerful electrical plates pulling and pushing her on the way to secure the sunken gold.
 
All that morning a fairly moderate rate of speed was maintained, as it was thought best not to run the new machinery too fast.
 
Dinner was eaten about a quarter of a mile below the surface, but no one inside the submarine would ever have known it. Electric lights made the place as brilliant as could be desired, and the food, which Tom and Mr. Damon prepared, was equal to any that could have been served on land. After the meal they opened the shutters⁶ over the windows in the sides of the craft, and looked at the myriads⁷ of fishes swimming past, as the creatures were disclosed in the glare of the searchlight.
 
That night they were several hundred miles on their journey, for the craft was speedy, and leaving Tom and Captain Weston to take the first watch, the others went to bed.
 
"Bless my soul, but it does seem odd, though, to go to bed under water, like a fish," remarked Mr. Damon. "If my wife knew this she would worry to death. She thinks I'm off automobiling. But this isn't half as dangerous as riding in a car that's always getting out of order. A submarine for mine, every time."
 
"Wait until we get to the end of this trip," advised Tom. "I guess you'll find almost as many things can happen in a submarine as can in an auto," and future events were to prove the young inventor to be right.
 
Everything worked well that night, and the ship made good progress. They rose to the surface the next morning to make sure of their position, and to get fresh air, though they did not really need the latter, as the reserve supply had not been drawn⁸ on, and was sufficient for several days, now that the oxygen machine had been put in running order.
 
On the second day the ship was sent to the bottom and halted there, as Mr. Swift wished to try the new diving suits. These were made of a new, light, but very strong metal to withstand the pressure of a great depth.
 
Tom, Mr. Sharp and Captain Weston donned the suits, the others agreeing to wait until they saw how the first trial resulted. Then, too, it was necessary for some one acquainted with the machinery to remain in the............