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Sciences_, whose _M้moires_ on the temperature of the Planetary spaces
appeared about 1827, reduced these figures to considerably diminished
proportions. According to his careful estimation, the temperature of
space is not much lower than 70 or 80 degrees Fahr. below zero."
"No more?" asked Ardan.
"No more," answered Barbican, "though I must acknowledge we have only
his word for it, as the _M้moire_ in which he had recorded all the
elements of that important determination, has been lost somewhere, and
is no longer to be found."
"I don't attach the slightest importance to his, or to any man's words,
unless they are sustained by reliable evidence," exclaimed M'Nicholl.
"Besides, if I'm not very much mistaken, Pouillet--another countryman of
yours, Ardan, and an Academician as well as Fourrier--esteems the
temperature of interplanetary spaces to be at least 256ฐ Fahr. below
zero. This we can easily verify for ourselves this moment by actual
experiment."
"Not just now exactly," observed Barbican, "for the solar rays,
striking our Projectile directly, would give us a very elevated instead
of a very low temperature. But once arrived at the Moon, during those
nights fifteen days long, which each of her faces experiences
alternately, we shall have plenty of time to make an experiment with
every condition in our favor. 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. For instance, you say, the
volume of _Uranus_ is 76 times greater than the Earth's; _Saturn's_ 900
times greater; _Jupiter's_ 1300 times greater; the Sun's 1300 thousand
times greater--You may tell me all that till I'm tired hearing it, and I
shall still be almost as ignorant as ever.
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