it uncomfortable to look at with the naked eye. But it
could illuminate matter only; the hard vacuum of space remained dark.
The pilot could have located the planets easily, without looking
around. He knew where each and every one of them were. He had to.

A man can navigate in space by instrument, and he can take the time to
figure out where every planet ought to be. But if he does, he won't
really be able to navigate in the Asteroid Belt.

In the Nineteenth Century, Mark Twain pointed out that a steamboat
pilot who navigated a ship up and down the Mississippi had to be able
to identify every landmark and every changing sandbar along the river
before he would be allowed to take charge of the wheel. He not only
had to memorize the whole river, but be able to predict the changes in
its course and the variations in its eddies. He had to be able to know
exactly where he was at every moment, even in the blackest of moonless
nights, simply by glancing around him.

An asteroid man has to be able to do the same thing. The human mind is
capable of it, and one thing that the men and women of the Belt Cities
had learned was to use the human mind.

"Looks like a big 'un, Jack," said the instrument man. His eyes were
on the radar screen. It not only gave him a picture of the body of the
slowly spinning mountain, but the distance and the angular and radial
velocities. A duplicate of the instrument gave the same information to
the pilot.

The asteroid was fairly large as such planetary debris went--some five
hundred meters in diameter, with a mass of around one hundred
seventy-four million metric tons.

* * * * *

Within twenty meters of the surface of the great mountain of stone,
the pilot brought the ship to a dead stop in relation to that surface.

"Looks like she's got a nice spin on her," he said. "We'll see."

He waited for what he knew would appear somewhere near the equator of
the slowly revolving mass. It did. A silvery splash of paint that had
originally been squirted on by the anchor man who had first spotted
the asteroid in order to check the rotational velocity.

The pilot of the space tug waited until the blotch was centered in the
crosshairs of his peeper and then punched the timer. When it came
around again, he would be able to compute the angular momentum of the
gigantic rock.

"Where's he got his anchor set?" the pilot asked his instrument man.

"The beep's from the Nort