I've trained and twenty more candidates. And I'd like to have some
decent rations! The last trip brought back two million bushels of
grain. You can certainly spare adequate food for twenty men for a few
days!"

It took some time to get the special device constructed, but the Med
Ship lifted in two days more. The device for which it had waited was
simply a preventive of the disaster overtaking the ship from the mine
on Orede. It was essentially a tank of liquid oxygen, packed in the
space from which stores had been taken away. When the ship's air
supply was pumped past it, first moisture and then CO_{2} froze out.

Then the air flowed over the liquefied oxygen at a rate to replace the
CO_{2} with more useful breathing material. Then the moisture was
restored to the air as it warmed again. For so long as the oxygen
lasted, fresh air for any number of men could be kept purified and
breathable. The Med Ship's normal equipment could take care of no more
than ten. But with this it could journey to Weald with almost any
complement on board.

Maril stayed on Dara when the Med Ship left. Murgatroyd protested
shrilly when he discovered her about to be closed out by the closing
airlock.

"_Chee!_" he said indignantly. "_Chee! Chee!_"

"No," said Calhoun. "We'll be crowded enough anyhow. We'll see her
later."

He nodded to one of the first four student pilots, who crisply made