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 could correctly register exceedingly low degrees of temperature.