and go forth before the moon had dropped so
far that the concentration in the condensers would fall below that
necessary to keep the portal from closing.

I took out also a small spectroscope, and a few other instruments for
the analysis of certain light manifestations and the testing of metal
and liquid. Finally, I put aside my emergency medical kit.

I had hardly finished examining and adjusting these before O'Keefe and
Huldricksson returned. They reported signs of a camp at least ten days
old beside the northern wall of the outer court, but beyond that no
evidence of others beyond ourselves on Nan-Tauach.

We prepared supper, ate and talked a little, but for the most part
were silent. Even Larry's high spirits were not in evidence; half a
dozen times I saw him take out his automatic and look it over. He was
more thoughtful than I had ever seen him. Once he went into the tent,
rummaged about a bit and brought out another revolver which, he said,
he had got from Da Costa, and a half-dozen clips of cartridges. He
passed the gun over to Olaf.

At last a glow in the southeast heralded the rising moon. I picked up
my instruments and the medical kit; Larry and Olaf shouldered each a
short ladder that was part of my equipment, and, with our electric
flashes pointing the way, walked up the great stairs, through the
enclosures, and straight to the grey stone.

By this time the moon had risen and its clipped light shone full upon
the slab. I saw faint gleams pass over it as of fleeting
phosphorescence--but so faint were they that I could not be sure of
the truth of my observation.

We set the ladders in place. Olaf I assigned to stand before the door
and watch for the first signs of its opening--if open it should. The
Becquerels were set within three-inch tripods, whose feet I had
equipped with vacuum rings to enable them to hold fast to the rock.

I scaled one ladder and fastened a condenser over the boss; descended;
sent Larry up to watch it, and, ascending the second ladder, rapidly
fixed the other in its place. Then, with O'Keefe watchful on his
perch, I on mine, and Olaf's eyes fixed upon the moon door, we began
our vigil. Suddenly there was an exclamation from Larry.

"Seven little lights are beginning to glow on this stone!" he cried.

But I had already seen those beneath my lens begin to gleam out with a
silvery lustre. Swiftly the rays within the condenser began to thicken
and increase, and as they did so th