"
I glanced at the thermometer. It registered 110 degrees. While
we were talking the mighty iron mole had bored its way over a mile
into the rock of the earth's crust.
"Let us continue on, then," I replied. "It should soon be over at
this rate. You never intimated that the speed of this thing would
be so high, Perry. Didn't you know it?"
"No," he answered. "I could not figure the speed exactly, for I
had no instrument for measuring the mighty power of my generator.
I reasoned, however, that we should make about five hundred yards
an hour."
"And we are making seven miles an hour," I concluded for him,
as I sat with my eyes upon the distance meter. "How thick is the
Earth's crust, Perry?" I asked.
"There are almost as many conjectures as to that as there
are geologists," was his answer. "One estimates it thirty miles,
because the internal heat, increasing at the rate of about one
degree to each sixty to seventy feet depth, would be sufficient to
fuse the most refractory substances at that distance beneath the
surface. Another finds that the phenomena of precession and nutation
require that the earth, if not entirely solid, must at least have
a shell not less than eight hundred to a thousand miles in thickness.
So there you are. You may take your choice."
"And if it should prove solid?" I asked.
"It will be all the same to us in the end, David," replied Perry.
"At the best our fuel will suffice to carry us but three or four
days, while our atmosphere cannot last to exceed three.
Pages:
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29