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.
"Right! that's correct!" he cried.
"You think so ?" asked Barbican.
"As true as Euclid!" exclaimed M'Nicholl.
"Wonderful fellows," murmured the Frenchman, smiling with admiration.
"You understand now, Ardan, don't you ?" asked Barbican.
"Don't I though ?" exclaimed Ardan, "why my head is splitting with it!" "Therefore," continued Barbican, " 2 10 r 1 10 r r 2v = 2gr {1 - -- --- - -- -- (-- --- - -- ---) } d 81 d d - r " "And now," exclaimed M'Nicholl, sharpening his pencil; "in order to obtain the velocity of the Projectile when leaving the atmosphere, we have only to make a slight calculation." The Captain, who before clerking on a Mississippi steamboat had been professor of Mathematics in an Indiana university, felt quite at home at the work.

He rained figures from his pencil with a velocity that would have made Marston stare.

Page after page was filled with his multiplications and divisions, while Barbican looked quietly on, and Ardan impatiently stroked his head and ears to keep down a rising head-ache.
"Well ?" at last asked Barbican, seeing the Captain stop and throw a somewhat hasty glance over his work.
"Well," answered M'Nicholl slowly but confidently, "the calculation is made, I think correctly; and _v_, that is, the velocity of the Projectile when quitting the atmosphere, sufficient to carry it to the neutral point, should be at least ..." "How much ?" asked Barbican, eagerly.
"Should be at least 11,972 yards the first second." "What!" cried Barbican, jumping off his seat.

"How much did you say ?" "11,972 yards the first second it quits the atmosphere." "Oh, malediction!" cried Barbican, with a gesture of terrible despair.
"What's the matter ?" asked Ardan, very much surprised.
"Enough is the matter!" answered Barbican excitedly.

"This velocity having been diminished by a third, our initial velocity should have been at least ..." "17,958 yards the first second!" cried M'Nicholl, rapidly flourishing his pencil.
"But the Cambridge Observatory having declared that 12,000 yards the first second were sufficient, our Projectile started with no greater velocity!" "Well ?" asked M'Nicholl.
"Well, such a velocity will never do!" "How?
?" } "How!!" } cried the Captain and Ardan in one voice.
"We can never reach the neutral point!" "Thunder and lightning" "Fire and Fury!" "We can't get even halfway!" "Heaven and Earth!" "_Mille noms d'un boulet!_" cried Ardan, wildly gesticulating.
"And we shall fall back to the Earth!" "Oh!" "Ah!" They could say no more.