inary propeller could not act, the
bullet may become a prime mover, and co-operate with the gun. A rocket
can burn without an atmosphere, and the recoil of the rushing fumes will
impel the car onwards."

_G_. "Do you think a rocket would have sufficient power to be of any
service?"

_I_. "Ten or twelve large rockets, capable of exerting a united back
pressure of one and a half tons during five or six minutes on a car of
that weight at the earth's surface, would give it in free space a
velocity of two miles a second, which, of course, would not be lost by
friction."

_G_. "So that it would not be absolutely necessary to give the
projectile an initial velocity of five miles a second."

_I_. "No; and, besides, we are not solely dependent on the rocket. A jet
of gas, at a very high pressure, escaping from an orifice into the
vacuum or ether, would give us a very high propelling force. By
compressing air, oxygen, or coal-gas (useful otherwise) in iron
cylinders with closed vents, which could be opened, we should have a
store of energy serviceable at any time to drive the car. In this way a
pressure or thrust of several tons on the square inch might be applied
to the car as long as we had gas to push it forwards."

_G_. "Certainly, and by applying the pressure, whether from the rocket
or the gas, to the front and sides, as well as to the rear of the car,
you would be able to regulate the speed, and direct the car wherever you
wanted to go."

_I_. "Moreover, beyond the range of gravitation, we could steer and
travel by pumping out the respired air, or occasionally projecting a
pebble from the car through a stuffing box in the wall, or else by
firing a shot from a pistol."

_G_. "You might even have a battery of machine guns on board, and
decimate the hosts of heaven."

_I_. "Our bullets would fly straight enough, anyhow, and I suppose they
would hit something in course of time."

_G_. "If they struck the earth they would be solemnly registered as
falling stars."

_I_. "Certainly they would be burnt up in passing through the atmosphere
of a planet and do no harm to its inhabitants."

_G_. "Well, now, granting that you could propel the car, and that
although your gun was badly aimed you could steer towards a planet, how
long would the journey take?"

_I_. "The self-movement of the car would enable us to save time, which
is a matter of the first importance on such a trip. In the plan of Jules
Verne, the bullet de