been dragged along with the comet, it has been calculated that at her
perihelion, or nearest point to the Sun, she would have to endure a heat
28,000 times greater than our mean summer temperature. But this heat,
fully capable of turning the rocks into glass and the oceans into vapor,
before proceeding to such extremity, must have first formed a thick
interposing ring of clouds, and thus considerably modified the excessive
temperature. Therefore, between the extreme cold of the aphelion and the
excessive heat of the perihelion, by the great law of compensation, it
is probable that the mean temperature would be tolerably endurable."

"At how many degrees is the temperature of the interplanetary space
estimated?" asked M'Nicholl.

"Some time ago," replied Barbican, "this temperature was considered to
be very low indeed--millions and millions of degrees below zero. But
Fourrier of Auxerre, a distinguished member of the _Académie des
Sciences_, whose _Mémoires_ 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 _Mémoire_ 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.