desire by means of a commutator in a convenient spot, for instance, at
the butt end of the gun, so as to follow up the bullet with ease, and
give it a planetary flight. By a proper adjustment of the solenoids and
currents, this could be done so gradually as to prevent a starting shock
to the occupants of the car. The velocity attained by the car would, of
course, depend on the number and power of the solenoids. If, for
example, each solenoid communicated to the car a velocity of nine yards
per second, a thousand solenoids, each magnetically stronger than
another in going from breech to muzzle, would be required to give a
final velocity of five miles a second. In such a case, the length of the
barrel would be at least 1,000 yards. Economy and safety would determine
the best proportions for the gun, but we are now considering the
feasibility of the project, not its cost. With regard to position and
supports, the gun might be constructed along the slope of a hill or
mound steep enough to give it the angle or elevation due to the aim. As
the barrel would not have to resist an explosive force, it should not be
difficult to make, and the inside could be lubricated to diminish the
friction of the projectile in passing through it. Moreover, it is
conceivable that the car need never touch the sides, for by a proper
adjustment of the magnetism of the solenoids we might suspend it in
mid-air like Mahomet's coffin, and make it glide along the magnetic axis
of the tube."

_G_. "It seems a promising idea for an actual gun, or an electric
despatch and parcel post, or even a railway. The bullet, I suppose,
would be of iron."

_I_. "Probably; but aluminium is magnetic in a lower degree than iron,
and its greater lightness might prove in its favour. We might also
magnetise the car, say by surrounding it with a coil of wire excited