Kinetic Energy Corporation in the twenty-first
century. Within the hollow double shell of a shelter-wall, or an
explorer's helmet-suit, or a space-flyer's hull, an oscillating
semi-vacuum current was maintained--an extremely rarified air,
magnetically charged, and maintained in rapid oscillating motion. Across
this field the outer cold, or heat, as the case might be, could
penetrate only with slow radiation. This Erentz system gave the most
perfect temperature insulation known in its day. Without it,
interplanetary flight would have been impossible.

And it served a double purpose. Developed at first for temperature
insulation only, the Erentz system surprisingly brought to light one of
the most important discoveries made in the realm of physics of the
century. It was found that any flashing, oscillating current, whether
electronic, or the semi-vacuum of rarified air--or even a thin sheet of
whirling fluid--gave also a pressure-insulation. The kinetic energy of
the rapid movement was found to absorb within itself the latent energy
of the unequal pressure.

(The intricate postulates and mathematical formulae necessary to
demonstrate the operation of the physical laws involved would be out of
place here.)

The _Planetara_ was so equipped, against the explosive tendency of its
inner air-pressures when flying in the near-vacuum of space. In the case
of Grantline's glassite shelters, the latent energy of his room interior
air pressure went largely into a kinetic energy which in practical
effect resulted only in the slight acceleration of the vacuum current,
and thus never reached the outer wall. The Erentz engineers claimed for
their system a pressure absorption of 97.4%, leaving, in Grantline's
case, only 2.6% of room pressure to be held by the building's aluminite
bracers.

It may be interesting to note in this connection that without the Erentz
system as a basis, the great sub-sea developments on Earth and Mars of
the twenty-first century would also have been impossible. Equipped with
a fluid circulation device of the Erentz principle within its double
hull, the first submarine was able to penetrate the great ocean deeps,
withstanding the tremendous ocean pressures at depths of four thousand
fathoms.

* * * * *

The work was over now. The borers had been dismantled and packed away.
At one end of the cliff the minin