第8章

Tom is Imprisoned

"Well, I must say he's a cool one," remarked Tom, as the echoes of Mr.Berg's steps died away."The idea of thinking his boat better than ours! I don't like that man, dad.I'm suspicious of him.Do you think he came here to steal some of our ideas?""No, I hardly believe so, my son.But how did you discover him?" "Just as you saw, dad.I heard a noise and went back there toinvestigate.I found him sneaking around, looking at the electric propeller plates.I went to grab him just as he stumbled over a hoard.At first I thought it was one of the old gang.I'm almost sure he was trying to discover something.""No, Tom.the firm he works for are good business men, and they would not countenance anything like that.They are heartless competitors, however, and if they saw a legitimate chance to get ahead of me and take advantage, they would do it.But they would not sneak in to steal my ideas.I feel sure of that.Besides, they have a certain type of submarine which they think is the best ever invented, and they would hardly change at this late day.They feel sure of winning the Government prize, and I'm just as glad we're not going to have a contest.""Do you think our boat is better than theirs?" "Much better, in many respects.""I don't like that man Berg, though," went on Tom.

"Nor do I," added his father."There is something strange about him.He was very anxious that I should compete.Probably he thought his firm's boat would go so far ahead of ours that they would get an extra bonus.But I'm glad he didn't see our new method of propulsion.That is the principal improvement in the Advance over other types of submarines.Well, another week and we will be ready for the test.""Have you known Mr.Berg long, dad?"

"Not very.I met him in Washington when I was in the patent office.He was taking out papers on a submarine for his firm at the same time Igot mine for the Advance.It is rather curious that he should come all the way here from Philadelphia.merely to see if I was going to compete.There is something strange about it, something that I can't understand."The time was to come when Mr.Swift and his son were to get at the bottom of Mr.Berg's reasons, and they learned to their sorrow that he had penetrated some of their secrets.

Before going to bed that night Tom and Mr.Sharp paid a visit to the shed where the submarine was resting on the ways, ready for launching.They found Mr.Jackson on guard and the engineer said that no one had been around.Nor was anything found disturbed.

"It certainly is a great machine," remarked the lad as he looked up at the cigar-shaped bulk towering over his head."Dad has outdone himself this trip.""It looks all right," commented Mr.Sharp."Whether it will work is another question.""Yes, we can't tell until it's in the water," con ceded Tom."But I hope it does.Dad has spent much time and money on it."The Advance was, as her name indicated, much in advance of previous submarines.There was not so much difference in outward construction as there was in the means of propulsion and in the manner in which the interior and the machinery were arranged.

The submarine planned by Mr.Swift and Tom jointly, and constructed by them, with the aid of Mr.Sharp and Mr.Jackson, was shaped like a Cigar, over one hundred feet long and twenty feet in diameter at the thickest part.It was divided into many compartments, all water-tight, so that if one or even three were flooded the ship would still be useable.

Buoyancy was provided for by having several tanks for the introduction of compressed air, and there was an emergency arrangement so that a collapsible aluminum container could be distended and filled with a powerful gas.This was to be used if, by any means, the ship was disabled on the bottom of the ocean.The container could be expanded and filled, and would send the Advance to the surface.

Another peculiar feature was that the engine-room, dynamos and other apparatus were all contained amidships.This gave stability to the craft,and also enabled the same engine to operate both shafts and propellers, as well as both the negative forward electrical plates, and the positive rear ones.

These plates were a new idea in submarine construction, and were the outcome of an idea of Mr.Swift, with some suggestions from his son.

The aged inventor did not want to depend on the usual screw propellers for his craft, nor did he want to use a jet of compressed air, shooting out from a rear tube, nor yet a jet of water, by means of which the creature called the squid shoots himself along.Mr.Swift planned to send the Advance along under water by means of electricity.

Certain peculiar plates were built at the forward and aft blunt noses of the submarine.Into the forward plate a negative charge of electricity was sent, and into the one at the rear a positive charge, just as one end of a horseshoe magnet is positive and will repel the north end of a compass needle, while the other pole of a magnet is negative and will attract it.In electricity like repels like, while negative and positive have a mutual attraction for each other.

Mr.Swift figured out that if he could send a powerful current of negative electricity into the forward plate it would pull the boat along, for water is a good conductor of electricity, while if a positive charge was sent into the rear plate it would serve to push the submarine along, and he would thus get a pulling and pushing motion, just as a forward and aft propeller works on some ferry boats.

But the inventor did not depend on these plates alone.There were auxiliary forward and aft propellers of the regular type, so that if the electrical plates did not work, or got out of order, the screws would serve to send the Advance along.