e; they did not twinkle because there was no atmosphere to
intervene with its strata unequally dense, and of different degrees of
humidity, which causes this scintillation.

The travellers long watched the constellated firmament, upon which the
vast screen of the moon made an enormous black hole. But a painful
sensation at length drew them from their contemplation. This was an
intense cold, which soon covered the glasses of the port-lights with a
thick coating of ice. The sun no longer warmed the projectile with his
rays, and it gradually lost the heat stored up in its walls. This heat
was by radiation rapidly evaporated into space, and a considerable
lowering of the temperature was the result. The interior humidity was
changed into ice by contact with the window-panes, and prevented all
observation.

Nicholl, consulting the thermometer, said that it had fallen to 17 deg.
(centigrade) below zero (1 deg. Fahr). Therefore, notwithstanding every
reason for being economical, Barbicane was obliged to seek heat as well
as light from gas. The low temperature of the bullet was no longer
bearable. Its occupants would have been frozen to death.

"We will not complain about the monotony of the journey," said Michel
Ardan. "What variety we have had, in temperature at all events! At times
we have been blinded with light, and saturated with heat like the
Indians of the Pampas! Now we are plunged into profound darkness amidst
boreal cold, like the Esquimaux of the pole! No, indeed! We have no
right to complain, and Nature has done many things in our honour!"

"But," asked Nicholl, "what is the exterior temperature?"

"Precisely that of planetary space," answered Barbicane.

"Then," resumed Michel Ardan, "would not this be an opportunity for
making that experiment we could not attempt when we were bathed in the
solar rays?"

"Now or never," answered Barbicane, "for we are usefully situated in
order to verify the temperature of space, and see whether the
calculations of Fourier or Pouillet are correct."

"Any way it is cold enough," said Michel. "Look at the interior humidity
condensing on the port-lights. If this fall continues the vapour of our
respiration will fall around us in snow."

"Let us get a thermometer," said Barbicane.

It will be readily seen that an ordinary thermometer would have given no
result under the circumstances in which it was going to be exposed. The
mercury would have frozen in its cup, for it does n