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.

There was much machinery in the submarine There were