long barrel, and a series of air chambers at intervals from the breech
to the muzzle. Each of these chambers, beginning at the breech, could be
opened in turn as the bullet passed along the barrel, so that every
escaping jet of gas would give it an additional impulse."

_G._ (_with growing interest_). "That sounds neater. You might work the
chambers by electricity."

_I_. "We could even have an electric gun. Conceive a bobbin wound with
insulated wire in lieu of thread, and having the usual hole through the
axis of the frame. If a current of electricity be sent through the wire,
the bobbin will become a hollow magnet or 'solenoid,' and a plug of soft
iron placed at one end will be sucked into the hole. In this experiment
we have the germ of a solenoid cannon. The bobbin stands for the
gun-barrel, the plug for the bullet-car, and the magnetism for the
ejecting force. We can arrange the wire and current so as to draw the
plug or car right through the hole or barrel, and if we have a series of
solenoids end to end in one straight line, we can switch the current
through each in succession, and send the projectile with gathering
velocity through the interior of them all. In practice the barrel would
consist of a long straight tube, wide and strong enough to contain the
bullet-car without flexure, and begirt with giant solenoids at
intervals. Each of the solenoids would be excited by a powerful current,
one after the other, so as to urge the projectile with accelerating
speed along the tube, and launch it into the vast."

_G_. "That looks still better than the pneumatic gun."

_I_. "A magnetic gun would have several advantages. For instance, the
currents can be sent through the solenoids in turn as quickly as we