Perry was becoming more hopeful, although upon what meager food he sustained his optimism I could not conjecture.  From cursing he had turned to singing—­I felt that the strain had at last affected his mind.  For several hours we had not spoken except as he asked me for the readings of the instruments from time to time, and I announced them.  My thoughts were filled with vain regrets.  I recalled numerous acts of my past life which I should have been glad to have had a few more years to live down.  There was the affair in the Latin Commons at Andover when Calhoun and I had put gunpowder in the stove—­and nearly killed one of the masters.  And then—­but what was the use, I was about to die and atone for all these things and several more.  Already the heat was sufficient to give me a foretaste of the hereafter.  A few more degrees and I felt that I should lose consciousness.

“What are the readings now, David?” Perry’s voice broke in upon my somber reflections.

“Ninety miles and 153 degrees,” I replied.

“Gad, but we’ve knocked that thirty-mile-crust theory into a cocked hat!” he cried gleefully.

“Precious lot of good it will do us,” I growled back.

“But my boy,” he continued, “doesn’t that temperature reading mean anything to you?  Why it hasn’t gone up in six miles.  Think of it, son!”

“Yes, I’m thinking of it,” I answered; “but what difference will it make when our air supply is exhausted whether the temperature is 153 degrees or 153,000?  We’ll be just as dead, and no one will know the difference, anyhow.”  But I must admit that for some unaccountable reason the stationary temperature did renew my waning hope.  What I hoped for I could not have explained, nor did I try.  The very fact, as Perry took pains to explain, of the blasting of several very exact and learned scientific hypotheses made it apparent that we could not know what lay before us within the bowels of the earth, and so we might continue to hope for the best, at least until we were dead—­when hope would no longer be essential to our happiness.  It was very good, and logical reasoning, and so I embraced it.

At one hundred miles the temperature had dropped to 152 1/2 degrees!  When I announced it Perry reached over and hugged me.

From then on until noon of the second day, it continued to drop until it became as uncomfortably cold as it had been unbearably hot before.  At the depth of two hundred and forty miles our nostrils were assailed by almost overpowering ammonia fumes, and the temperature had dropped to ten below zero!  We suffered nearly two hours of this intense and bitter cold, until at about two hundred and forty-five miles from the surface of the earth we entered a stratum of solid ice, when the mercury quickly rose to 32 degrees.  During the next three hours we passed through ten miles of ice, eventually emerging into another series of ammonia-impregnated strata, where the mercury again fell to ten degrees below zero.