hat it was so cold."

His teeth actually chattered so much that he could hardly articulate;
still he, as well as the others, disliked to entrench on their short
supply of gas.

"One feature of our journey that I particularly admire," said Ardan,
trying to laugh with freezing lips, "is that we can't complain of
monotony. At one time we are frying with the heat and blinded with the
light, like Indians caught on a burning prairie; at another, we are
freezing in the pitchy darkness of a hyperborean winter, like Sir John
Franklin's merry men in the Bay of Boothia. _Madame La Nature_, you
don't forget your devotees; on the contrary, you overwhelm us with your
attentions!"

"Our external temperature may be reckoned at how much?" asked the
Captain, making a desperate effort to keep up the conversation.

"The temperature outside our Projectile must be precisely the same as
that of interstellar space in general," answered Barbican.

"Is not this precisely the moment then," interposed Ardan, quickly,
"for making an experiment which we could never have made as long as we
were in the sunshine?"

"That's so!" exclaimed Barbican; "now or never! I'm glad you thought of
it, Ardan. We are just now in the position to find out the temperature
of space by actual experiment, and so see whose calculations are right,
Fourier's or Pouillet's."

"Let's see," asked Ardan, "who was Fourier, and who was Pouillet?"

"Baron Fourier, of the French Academy, wrote a famous treatise on
_Heat_, which I remember reading twenty years ago in Penington's book
store," promptly responded the Captain; "Pouillet was an eminent
professor of Physics at the Sorbonne, where he died, last year, I
think."

"Thank you, Captain," said Ardan; "the cold does not injure your memory,
though it is decidedly on the advance. See how thick the ice is already
on the window panes! Let it only keep on and we shall soon have our
breaths falling around us in flakes of snow."

"Let us prepare a thermometer," said Barbican, who had already set
himself to work in a business-like manner.

A thermometer of the usual kind, as may be readily supposed, would be of
no use whatever in the experiment that was now about to be made. In an
ordinary thermometer Mercury freezes hard when exposed to a temperature
of 40 deg. below zero. But Barbican had provided himself with a _Minimum_,
_self-recording_ thermometer, of a peculiar nature, invented by
Wolferdin, a friend of Arago's, which