The air here on the Moon surface was negligible—a scant one five-thousandth of the atmospheric pressure at the sea-level on Earth. But within the glassite shelter, a normal Earth-pressure must be maintained. Rigidly braced double walls to withstand the explosive tendency, with no external pressure to counteract it. A tremendous necessity for mechanical equipment had burdened Grantline's small ship to its capacity. The chemistry of manufactured air, the pressure equalizers, renewers, respirators, the lighting and temperature-maintenance systems—all the mechanics of a space-flyer were here.
And within the glassite double walls, there was necessity for a constant circulation of the Erentz temperature insulating system.[D]
There was this main Grantline building, stretching low and rectangular along the front edge of the ledge. Within it were living rooms, messroom and kitchen. Fifty feet behind it, connected by a narrow passage of glassite, was a similar, though smaller structure. The mechanical control rooms, with their humming, vibrating mechanisms were here. And an instrument room with signaling apparatus, senders, receivers, mirror-grids and audiphones of several varieties; and an electro-telescope, small but modern, with dome overhead like a little Earth observatory.
From this instrument building, beside the connecting pedestrian passage, wire cables for light, and air-tubes and strings and bundles of instrument wires ran to the main structure—gray snakes upon the porous, gray Lunar rock.
The third building seemed a lean-to banked against the cliff-wall, a slanting shed-wall of glassite fifty feet high and two hundred in length. Under it, for months Grantline's borers had dug into the cliff. Braced tunnels were here, penetrating back and downward into this vein of radio-active rock.
The work was over now. The borers had been dismantled and packed away. At one end of the cliff the mining equipment lay piled in a litter. There was a heap of discarded ore where Grantline had carted and dumped it after his first crude refining process had yielded it as waste. The ore-slag lay like gray powder-flakes strewn down the cliff. Tracks and ore-carts along the ledge stood discarded, mute evidence of the weeks and months of work these helmeted miners had undergone, struggling upon this airless, frowning world.
But now all that was finished. The radio-active ore was sufficiently concentrated. It lay—this treasure—in a seventy-foot pile behind the glassite lean-to, with a cage of wires over it and an insulation barrage guarding its Gamma rays from escaping to mark its presence.
The ore-shelter was dark; the other two buildings were lighted. And there were small lights mounted at intervals about the camp and along the edge of the ledge. A spider ladder, with tiny platforms some twenty feet one above the other, hung precariously to the cliff-face. It descended the five hundred feet to the crater floor; and, behind the camp, it mounted the jagged cliff-face to the upper rim-height, where a small observatory platform was placed.