"According to your system," said my uncle; "but what does the thermometer say?"
"Scarcely 15 degrees by Reaumur, which is only an increase of 9 since our departure."
"Well, and what conclusion does that bring you to?" inquired the Professor.
"The deduction I draw from this is very simple. According to the most exact observations, the augmentation of the temperature of the interior of the earth is 1 degree for every hundred feet. But certain local causes may considerably modify this figure. The difference evidently depends on the conductibility of certain rocks. In the neighborhood of an extinct volcano, it has been remarked that the elevation of temperature was only 1 degree in every 125 feet. Let us, then, go upon this calculation—which is the most favorable—and calculate."
"Calculate away, my boy."
"Nothing easier," said I, pulling out my note-book and pencil. Nine times one hundred and twenty-five feet, make a depth of eleven hundred and twenty-five feet."
"Archimedes could not have spoken more geometrically."
"Well?"
"Well, according to my observations, we are at least ten thousand feet below the level of the sea."
"Can it be possible?"
"Either my calculation is correct, or there is no truth in figures."
The calculations of the Professor were perfectly correct. We were already six thousand feet deeper down in the bowels of the earth than anyone had ever been before. The lowest known depth to which man had hitherto penetrated was in the mines of Kitz-Bahl, on the Tyrol, and those of Württemburg in Bohemia.
The temperature, which should have been eighty-one, was in this place only fifteen. This was a matter for serious consideration.
