angular changes to give a three-dimensional picture of the nearer
heavens.

It was a highly necessary art which had not been worked out on Dara,
and the prospective astrogators became absorbed in this and other fine
points of space-piloting. They'd done enough, in a few trips to Orede,
to realize that they needed to know more. Calhoun showed them.

Calhoun did not try to make things easy for them. He was hungry and
easily annoyed. It was sound training tactics to be severe, and to
phrase all suggestions as commands. He put the four young men in
command of the ship in turn, under his direction. He continued to use
Weald as a destination, but he set up problems in which the Med Ship
came out of overdrive pointing in an unknown direction and with a
precessory motion.

He made the third of his students identify Weald in the celestial
globe containing hundreds of millions of stars, and get on course in
overdrive toward it. The fourth was suddenly required to compute the
distance to Weald from such data as he could get from observation,
without reference to any records.

By this time the first man was chafing to take a second turn. Calhoun
gave each of them a second gruelling lesson. He gave them, in fact, a
highly condensed but very sound course in the art of travel in space.
His young students took command in four-hour watches, with at least
one breakout from overdrive in each watch.

He built up enthusiasm in them. They ignored the discomfort of being
hungry--though there had been no reason for them to stint on food on