Slowly it rose once more until we were convinced that at last we were nearing the molten interior of the earth.  At four hundred miles the temperature had reached 153 degrees.  Feverishly I watched the thermometer.  Slowly it rose.  Perry had ceased singing and was at last praying.

Our hopes had received such a deathblow that the gradually increasing heat seemed to our distorted imaginations much greater than it really was.  For another hour I saw that pitiless column of mercury rise and rise until at four hundred and ten miles it stood at 153 degrees.  Now it was that we began to hang upon those readings in almost breathless anxiety.

One hundred and fifty-three degrees had been the maximum temperature above the ice stratum.  Would it stop at this point again, or would it continue its merciless climb?  We knew that there was no hope, and yet with the persistence of life itself we continued to hope against practical certainty.

Already the air tanks were at low ebb—­there was barely enough of the precious gases to sustain us for another twelve hours.  But would we be alive to know or care?  It seemed incredible.

At four hundred and twenty miles I took another reading.

“Perry!” I shouted.  “Perry, man!  She’s going down!  She’s going down!  She’s 152 degrees again.”

“Gad!” he cried.  “What can it mean?  Can the earth be cold at the center?”

“I do not know, Perry,” I answered; “but thank God, if I am to die it shall not be by fire—­that is all that I have feared.  I can face the thought of any death but that.”

Down, down went the mercury until it stood as low as it had seven miles from the surface of the earth, and then of a sudden the realization broke upon us that death was very near.  Perry was the first to discover it.  I saw him fussing with the valves that regulate the air supply.  And at the same time I experienced difficulty in breathing.  My head felt dizzy—­my limbs heavy.

I saw Perry crumple in his seat.  He gave himself a shake and sat erect again.  Then he turned toward me.

“Good-bye, David,” he said.  “I guess this is the end,” and then he smiled and closed his eyes.

“Good-bye, Perry, and good luck to you,” I answered, smiling back at him.  But I fought off that awful lethargy.  I was very young—­I did not want to die.

For an hour I battled against the cruelly enveloping death that surrounded me upon all sides.  At first I found that by climbing high into the framework above me I could find more of the precious life-giving elements, and for a while these sustained me.  It must have been an hour after Perry had succumbed that I at last came to the realization that I could no longer carry on this unequal struggle against the inevitable.