[A] The principle of this invisible cloak involves the use of an electronized fabric. All color is absorbed. The light rays reflected to the eye of the observer thus show an image of empty blackness. There is also created about the cloak a magnetic field which by natural laws bends the rays of light from objects behind it. This principle of the natural bending of light when passing through a magnetic field was first recognized by Albert Einstein, a scientist of the Twentieth century. In the case of this invisible cloak, the bending light rays, by making visible what was behind the cloak's blackness, thus destroyed its solid black outline and gave a pseudo-invisibility which was fairly effective under favorable conditions.
[B] An allusion to the use of the zed-ray light for making spectro-photographs of what might be behind obscuring rock masses, similar to the old-style X-ray.
[C] About fifty miles.
[D] An intricate system of insulation against extremes of temperature, developed by the Erentz 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.
[E] Within the Grantline buildings it was found more convenient to use a gravity normal to Earth. This was maintained by the wearing of metal-weighted shoes and metal-loaded belt. The Moon-gravity is normally approximately one-sixth the gravity of Earth.
[F] The Gravely storage tanks—the power used by the Grantline expedition—were heavy and bulky affairs. Economy of space on the Comet allowed but few of them.