even, by a sufficient expenditure of mental energy,
materialize a planet around your ship and crush it. However, these crude
methods are distasteful in the extreme, especially since you have
already given me some slight and unexpected mental exercise. In return,
I shall give you one chance for your lives. I cannot dematerialize
either you or your vessel until I work out the formula for your peculiar
atomic structure. If I can derive the formula before you reach the
boundaries of my home-space, beyond which I cannot go, I shall let you
go free. Deriving the formula will be a neat little problem. It should
be fairly easy, as it involves only a simple integration in ninety-seven
dimensions."

* * * * *

Silence ensued, and Seaton advanced his lever to the limit of his
ability to retain consciousness. Almost overcome by the horror of their
position, in an agony of suspense, expecting every instant to be hurled
into nothingness, he battled on, with no thought of yielding, even in
the face of those overwhelming mental odds.

"You can't do it, old top," he thought savagely, concentrating all the
power of his highly-trained mind against the intellectual monster. "You
can't dematerialize us, and you can't integrate above ninety-five
dimensions to save your neck. You can't do it--you're slipping--you're
all balled up right now!"

For more than an hour the silent battle raged, during which time the
Skylark flew millions upon millions of miles toward Earth. Finally the
stranger spoke again.

"You three win," it said abruptly. In answer to the unspoken surprise of
all three men it went on: "Yes, all three of you got the same idea and
Crane even forced his body to retain consciousness to fight me. Your
efforts were very feeble, of course, but were enough to interrupt my
calculations at a delicate stage, every time. You are a low form of
life, undoubtedly, but with more mentality than I supposed at first. I
could get that formula, of course, in spite of you, if I had time, but
we are rapidly approaching the limits of my territory, outside of which
even I could not think my way back. That is one thing in which your
mechanical devices are superior to anything my own race developed before
we became pure intellectuals. They point the way back to your Earth,
which is so far away that even my mentality cannot grasp the meaning of
the distance. I can understand the Earth, can visualize it from your
minds,