Chapter Four. Tom is Imprisoned - Page 2

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