"Very well," continued Barbican. "Now _m_ prime over _m_, that is the
ratio of the Moon's mass to that of the Earth is about the 1/81. _g_
gravity being at Florida about 32-1/4 feet, of course _g_ x _r_ must
be--how much, Captain?"

"38,465 miles," replied M'Nicholl.

"Now then?" asked Ardan.

[Illustration: MY HEAD IS SPLITTING WITH IT.]

"Now then," replied Barbican, "the expression having numerical values, I
am trying to find _v_, that is to say, the initial velocity which the
Projectile must possess in order to reach the point where the two
attractions neutralize each other. Here the velocity being null, _v_
prime becomes zero, and _x_ the required distance of this neutral point
must be represented by the nine-tenths of _d_, the distance between the
two centres."

"I have a vague kind of idea that it must be so," said Ardan.

"I shall, therefore, have the following result;" continued Barbican,
figuring up; "_x_ being nine-tenths of _d_, and _v_ prime being zero, my
formula becomes:--

2 10 r 1 10 r r
v = gr {1 - ----- - ---- (----- - -----) }
d 81 d d - r "

The Captain read it off rapidly.