The morning meal was not quite ready, when Barbican, raising his head,
showed Ardan a page covered with algebraic signs at the end of which
stood the following formula:--

1 2 2 r m' r r
--- (v' - v ) = gr {--- - 1 + --- (----- - -----) }
2 x m d - x d - r

"Which means?" asked Ardan.

"It means," said the Captain, now taking part in the discussion, "that
the half of _v_ prime squared minus _v_ squared equals _gr_ multiplied
by _r_ over _x_ minus one plus _m_ prime over _m_ multiplied by _r_ over
_d_ minus _x_ minus _r_ over _d_ minus _r_ ... that is--"

"That is," interrupted Ardan, in a roar of laughter, "_x_ stradlegs on
_y_, making for _z_ and jumping over _p_! Do _you_ mean to say you
understand the terrible jargon, Captain?"

"Nothing is clearer, Ardan."

"You too, Captain! Then of course I must give in gracefully, and declare
that the sun at noon-day is not more palpably evident than the sense of
Barbican's formula."

"You asked for Algebra, you know," observed Barbican.

"Rock crystal is nothing to it!"

"The fact is, Barbican," said the Captain, who had been looking over the