ompletely bald, not even a fringe of hair remaining. It gleamed in
the light of the desk lamp. Presently the bald pate revolved back and
a truculent face stared up at them.

Dr. Marks looked like a man who had been born impatient. His
underslung jaw thrust forward as he demanded, "Well, well? What is
this, Dodd? Well? Who are these people?"

Dodd was unperturbed. "Dr. Brant, Dr. Weiss, and Richard Brant and
Donald Scott."

Marks harrumphed. He stood erect, and he was scarcely taller than
little Julius Weiss. He had a solid, square build and massive hands.
"I am honored, gentlemen," he said crisply. "Sit down."

The Spindrifters did so. "We will get to business," Marks stated. "You
will forgive me if I begin on an elementary level. It is only for the
purpose of defining the problem. Ames said you had been briefed by
Miller, so I will confine the briefing to my part of the project."

Hartson Brant and Julius Weiss produced notebooks. Rick and Scotty
relaxed as best they could in the uncomfortable chairs and prepared to
listen.

"You are, of course, aware of the problems inherent in the development
of inertial systems," Marks began. "Perturbations are many, and both
predictable and random. Consider our missile. We set its little brain
for a given pattern. We depend on its inertia to inform the brain when
perturbations are pulling it off course. The brain then takes the
necessary corrective action. This, of course, is oversimplification."

It wasn't very simple to Rick. He squirmed uncomfortably on the hard
chair.

"Now, we have dealt primarily with the perturbations one would expect.
The equatorial bulge, for example. The result? We still have a
probable error of several miles in hitting the target. This is not to
be borne, gentlemen. We must have precision. Now, what information do
we have that allows such precision? We have the effects of
perturbation of the other planetary bodies and of the sun itself.
These we may calculate closely. We shall use them to guide our
missile, as they interact with the missile's own inertia."

Marks broke off to glare at Rick. He inquired acidly, "Do I perhaps
bore you? Or have you a serious itch? If so, scratch it, for heaven's
sake. You are squirming so, I can see only a blur through the corner
of my eye."

Hartson Brant came to his son's rescue. He looked at Dodd. "May the
boys be excused? I'm sure this discussion will be of no value to them,
and probably they have some thin