nabled 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.

There was much machinery in the submarine There were gasolene motors,
since space was too cramped to allow the carrying of coal for boilers.
There were dynamos, motors and powerful pumps. Some of these were for
air, and some for water. To sink the submarine below the surface large
tanks were filled with water. To insure a more sudden descent,
deflecting rudders were also used, similar to those on an airship.
There were also special air pumps, and one for the powerful gas, which
was manufactured on board.

Forward from the engine-room was a cabin, where meals could be served,
and where the travelers could remain in the daytime. There was also a
small cooking galley, or kitchen, there. Back of the engine-