To be sure, our Satellite is at present moving in a vacuum." "A vacuum ?" asked Ardan; "a perfect vacuum ?" "Well, a perfect vacuum as far as air is concerned." "But is the air replaced by nothing ?" "Oh yes," replied Barbican.

"By ether." "Ah, ether! and what, pray, is ether ?" "Ether, friend Michael, is an elastic gas consisting of imponderable atoms, which, as we are told by works on molecular physics, are, in proportion to their size, as far apart as the celestial bodies are from each other in space.

This distance is less than the 1/3000000 x 1/1000', or the one trillionth of a foot.

The vibrations of the molecules of this ether produce the sensations of light and heat, by making 430 trillions of undulations per second, each undulation being hardly more than the one ten-millionth of an inch in width." "Trillions per second! ten-millionths of an inch in width!" cried Ardan.
"These oscillations have been very neatly counted and ticketed, and checked off! Ah, friend Barbican," continued the Frenchman, shaking his head, "these numbers are just tremendous guesses, frightening the ear but revealing nothing to the intelligence." "To get ideas, however, we must calculate--" "No, no!" interrupted Ardan: "not calculate, but compare.

A trillion tells you nothing--Comparison, everything.