t was deadly.

On the other hand, the Satorians were not entirely in the dark as to the
progress of Nansal, as Arcot and Morey discovered one day.

After months of work designing and tooling up the Nansalian factories,
making the tools to make the tools to make the war material needed, and
training the engineers of Nansal all over the planet to produce the
equipment needed, Arcot and Morey finally found time to take a few days
off.

Tharlano had begun a systematic search of the known nebulae, comparing
them with the photographs the Earthmen had given him, and looking for a
galaxy with two satellite star clouds of exactly the right size and
distance from the great spiral.

After months of work, he had finally picked one which filled the bill
exactly! He invited Arcot and Morey to the observatory to confirm his
findings.

The observatory was located on the barren peak of a great mountain more
than nine miles high. It was almost the perfect place for an
astronomical telescope. Here, well above the troposphere, the air was
thin and always clear. The solid rock of the mountain was far from
disturbing influences which might cause any vibration in the telescope.

The observatory was accessible only from a spaceship or air flyer, and,
at that altitude, had to be pressurized and sealed against the thin,
cold air outside. Within, the temperature was kept constant to a
fraction of a degree to keep thermal expansion from throwing the mirror
out of true.

Arcot and Morey, accompanied by Tharlano and Torlos, settled the
_Ancient Mariner_ to the landing field that had been blasted out of the
rock of the towering mountain. They went over to the observatory and
were at once admitted to the airlock.

The floor was of smoothed, solid rock, and in this, the great clock
which timed and moved the telescope was set.

The entire observatory was, of course, surrounded by a magnetic shield,
and it was necessary to make sure there were no enemy ships around
before using the telescope, because the magnetic field affected the
light rays passing through it.

The mirror for the huge reflecting telescope was nearly three hundred
inches in diameter, and was powerful enough to spot a spaceship leaving
Sator. Its military usefulness, however, was practically nil, since
painting the ships black made them totally invisible.

There were half a dozen assistants with Tharlano at the observatory at
all times, one of them in charge of the great fi