a guess, Dad, though there was some logic
behind the thought. You ought to be able to trace down the idea! How
about you, Morey?" Arcot smiled at his friend.

"I've kept discreetly quiet," replied Morey, "feeling that in silence I
could not betray my ignorance, but since you ask me, I can guess too. I
seem to recall that light is affected by a powerful magnet, and I can
imagine that that was the basis for your guess. It has been known for
many years, as far back as Clerk Maxwell, that polarized light can be
rotated by a powerful magnet."

"That's it! And now we may as well go over the whole story, and tell Dad
and your father all that happened. Perhaps in the telling, we can
straighten out our own ideas a bit."

For the next hour the three men talked, each telling his story, and
trying to explain the whys and wherefores of what he had seen. In the
end all agreed on one point: if they were to fight this enemy, they
_must_ have ships that could travel though space with speed to match
that of the invaders, ships with a self-contained source of power.

During a brief lull in the conversation, Morey commented rather
sarcastically: "I wonder if Arcot will now kindly explain his famous
invisible light, or the lost star?" He was a bit nettled by his own
failure to remember that a star could go black. "I can't see what
connection this has with their sudden attack. If they were there, they
must have developed when the star was bright, and as a star requires
millions of years to cool down, I can't see how they could suddenly
appear in space."

Before answering, Arcot reached into a drawer of his desk and pulled out
an old blackened briar pipe. Methodically he filled it, a thoughtful
frown on his face; then carefully lighting it, he leaned back, puffing
out a thin column of gray smoke.

"Those creatures must have developed on their planets before the sun
cooled." He puffed slowly. "They are, then, a race millions of years
old--or so I believe. I can't give any scientific reason for this
feeling; it's merely a hunch. I just have a feeling that the invaders
are old, older than our very planet! This little globe is just about two
billion years old. I feel that that race is so very ancient they may
well have counted the revolutions of our galaxy as, once every twenty or
thirty million years, it swung about its center.

"When I looked at those great machines, and those comparatively little
beings as they handled their projectors