n observers saw the enemy ship now with their 'scopes gazing
directly along our Benson-light. And Drac was calling, "I've got the
measurement of its velocity. Doubling every ten seconds. God, what
acceleration!"

I flung off the Benson-light. The enemy ship had come from behind the
limb of the Moon; our straight-light telescopes showed it clearly. It
was heading unmistakably in our direction.

Drac was pleading, "We need velocity! Are you coming to the turret?"

"Yes."

Grantline and I rushed out upon the catwalk. Waters was mounting the
spiral ladder from the deck. "Into your cubby," I shouted. "Call
Earth. Keep calling until you get them."

Grantline rushed for the deck. I gained the control turret, Drac, with
his thin face white and set, met me at the door. "We need velocity."

I nodded. "We'll get it, Drac; have no fear of that."

I set the gravity-plates for the greatest possible acceleration
forward and added the stern rocket engines for narrow-angle
maneuvering.

With gathering speed we plunged directly for the oncoming enemy ship.

6

"But there's something wrong, Drac."

"We've got grade five acceleration."

Grantline had joined us in the control turret. "How far would you say,
at a rough guess, that ship is from us now?"

"Thirty thousand miles; about that." Drac scanned his page of
calculations. "Impossible to gauge with any exactness; they change
their pace so often and I can't figure out how large the damn thing
is."

"Say they've got a forty thousand velocity; added to our ten, that's
fifty."

"And we're accelerating. In half an hour we'll be within range."

"But there's something wrong," I persisted.

For several minutes now I had been aware that the _Cometara_ was
acting strangely. A sluggish response to the controls, I thought, but
when I called engine chief Franklin, he had not noticed it. Yet I was
certain.

Grantline stared at me. "Something wrong?"

"Yes. Drac, try orienting us. I did it ten minutes ago." I shoved him
at my equations, giving the angles with the Sun, Earth and Moon which
we should now have. "There's our flight course as it ought to be.
Measure how we're heading, actual position. If it's what it ought to
be, with the plate-combinations I'm using, then I'm crazy."

"Oh, you're just naturally apprehensive," Grantline said.

But we were not where we should be. The _Cometara_ was off her
predetermined course. And then I realized the factor of error. The