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. Neither,

then, is sufficient to bear us in the safety through eight thousand

miles of rock to the antipodes."

"If the crust is of sufficient thickness we shall come to a final

stop between six and seven hundred miles beneath the earth's surface;

but during the last hundred and fifty miles of our journey we shall

be corpses. Am I correct?" I asked.

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