hey turned them back with tractor and pressor beams. They drove
for us, sir, to try to destroy us with our own bombs, because they didn't
have any of their own."

The skipper's mouth opened and closed.

"Another item, sir," said Baird more uncomfortably still. "They don't use
iron or steel. Every metal object I saw was either a bronze or a light
metal. I suspect some of their equipment's made of potassium, and I'm
fairly sure they use sodium in the place of aluminum. Their atmosphere's
quite different from ours--obviously! They'd use bronze for their ship's
hull because they can venture into an oxygen atmosphere in a bronze ship.
A sodium-hulled ship would be lighter, but it would burn in oxygen. Where
there was moisture--"

The skipper blinked.

"_But they couldn't drive in a non-magnetic hull!_" he protested. "_A
ship has to be magnetic to drive!_"

"Sir," said Baird, his voice still shaken, "they don't use a magnetronic
drive. I once saw a picture of the drive they use, in a stereo on the
history of space travel. The principle's very old. We've practically
forgotten it. It's a Dirac pusher-drive, sir. Among us humans, it came
right after rockets. The planets of Sol were first reached by ships using
Dirac pushers. But--" He paused. "They won't operate in a magnetic field
above seventy Gauss, sir. It's a static-charge reaction, sir, and in a
magnetic field it simply stops working."

The skipper regarded Baird unwinkingly for a long time.

"_I think you are telling me_," he said at long last, "_that the Plumies'
drive would work if they were cut free of the _Niccola_._"

"Yes, sir," said Baird. "Their engineers were opening up the
drive-elements and checking them, and then closing them up again. They
couldn't seem to find anything wrong. I don't think they know what the
trouble is. It's the _Niccola's_ magnetic field. I think it was our field
that caused the collision by stopping their drive and killing all their
controls when they came close enough."

"_Did you tell them?_" demanded the skipper.

"There was no easy way to tell them by diagrams, sir."

Taine's voice cut in. It was feverish. It was strident. It was
triumphant.

"_Sir! The _Niccola_ is effectively a wreck and unrepairable. But the
Plumie ship is operable if cut loose. As weapons officer, I intend to
take the Plumie ship, let out its air, fill its tanks with our air, start
up its drive, and turn it over to you for navigation back to base!_"