Page:Tom Swift and His Submarine Boat.djvu/43

Rh 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