“It did not melt my lead or my sounding-wire,” said he. And as he said these words her heart fell.
The temperature of this great perforation was taken at many points, and when Roland brought to Margaret the statement of the height of the mercury at the very bottom she was astounded and shocked to find that it was only eighty-three degrees.
“This is terrible!” she ejaculated.
“What do you mean?” he asked in surprise. “That is not hot. Why, it is only summer weather.”
But she did not think it terrible because it was so hot; the fact that it was so cool had shocked her. In such temperature one could live! A great source of trust and hope had been taken from her.
“Roland,” she said, sinking into a chair, “I don't understand this at all. I always thought that it became hotter and hotter as one went down into the earth; and I once read that at twenty miles below the surface, if the heat increased in proportion as it increased in a mine, the temperature must be over a thousand degrees Fahrenheit. Your instrument could not have registered properly; perhaps it never went all the way down; and perhaps it is all a mistake. It may be that the lead did not go down so far as you think.”
He smiled; he was becoming calmer now, for he was doing something: he was obtaining results.
“Those ideas about increasing heat at increasing depths are old-fashioned, Margaret,” he said. “Recent science has given us better theories. It is known that there is great heat in the interior of the earth, and it is also known that the transmission of this heat towards the surface depends upon the conductivity of the rocks in particular locations. In some places the heat comes very near the surface, and in others it is very, very far down. More than that, the temperature may rise as we go down into the earth and afterwards fall again. There may be a stratum of close-grained rock, possibly containing metal, coming up from the interior in an oblique direction and bringing the heat towards the surface; then below that there may be vast regions of other rocks which do not readily conduct heat, and which do not originate in heated portions of the earth's interior. When we reach these, we must find the temperature lower, as a matter of course. Now I have really done this. A little over five miles down my thermometer registered ninety-one, and after that it began to fall a little. But the rocks under us are poor conductors of heat; and, moreover, it is highly probable that they have no near communication with the source of internal heat.”
“I thought these things were more exact and regular,” said she; “I supposed if you went down a mile in one place, you would find it as hot as you would in another.”
“Oh no,” said he. “There is nothing regular or exact in nature; even our earth is not a perfect sphere. Nature is never mathematically correct. You must always allow for variations. In some parts of the earth its heated core, or whatever it is, must be very, very far down.”