"Now that the expressions are reduced to figures, I am going to find the velocity v zero—that is to say, the velocity that the projectile ought to have on leaving the atmosphere to reach the point of equal attraction with no velocity. The velocity at that point I make equal zero, and x, the distance where the neutral point is, will be represented by the nine-tenths of d—that is to say, the distance that separates the two centres."
"I have some vague idea that it ought to be so," said Michel.
"I shall then have, x equals nine-tenths of d, and v equals zero, and my formula will become—"
Barbicane wrote rapidly on the paper—
2 10r 1 10r r
v = 2 gr { 1 - —- —- ( —- - —-) }
0 9d 81 d d-r
Nicholl read it quickly.
"That's it! that is it!" he cried.
"Is it clear?" asked Barbicane.
"It is written in letters of fire!" answered Nicholl.
"Clever fellows!" murmured Michel.