eight 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