etism there were both negative and positive fields
manifesting themselves in the form of attraction and repulsion. These
opposing characteristics were the basis for man's mastery of electrical
machinery.

But for gravitation, there had seemed at first no means of manipulating
it. As it was to develop, this was due to two factors. First, the Earth
itself possessed a gravitational phenomenon in this force outside of
that intense, all-pervading field. Second, to overcome this primal force
required the application of energy on such scales as could not be found
outside of the mastery of nuclear energy.

There was a simple parallel, Burl had been told the day before by Sam
Oberfield, in the history of aviation. A practical, propeller-driven
flying machine could not be constructed until a motor had been invented
that was compact, light and powerful enough to operate it. So all
efforts to make such machines prior to the development of the internal
combustion engine in the first days of the twentieth century were doomed
to failure. Likewise, in this new instance, a machine to utilize
gravitation could not be built until a source of power was developed
having the capacity to run it. Such power was found only in the
successful harnessing of the hydrogen disintegration explosion--the
H-bomb force. The first success at channeling this nuclear power in a
nonbomb device had been accomplished in England in 1958. The Zeta-ring
generator had been perfected in the next decade.

Only this source of harnessed atomic power could supply the force
necessary to drive an A-G ship.

The nose of the _Magellan_ housed an H-power stellar generator. Within
the bulk of the top third of the ship was this massive power source, its
atomic components, its uranium-hydrogen fuel, and the beam that
channeled the gravitational drive.

"Negating gravity is not a simple matter like inventing a magic sheet of
metal that cuts off the pull of the Earth, such as H. G. Wells wrote
about," Oberfield had explained. "That is impossible because it ignores
all the other laws of nature; it forgets the power of inertia, it denies
the facts of mass and density. It takes just as much energy to lift an
anti-gravity ship as to lift a rocketship. The difference is only in the
practicality of the power source. A rocketship must burn its fuel by
chemical explosion in order to push its cargo load upward. Its fuel is
limited by its own weight and by the awkwardness of its hand