"In one of his experiments, the pressure was reduced to 246 millimeters—9.7 inches.
"'This,' he says, 'is exactly the pressure on the highest summit of the Himalayas—the same degree of pressure which was so near proving fatal to Glaisher and Coxwell; I reached this point without the slightest sense of discomfort, or, to speak more accurately, the unpleasant sensations I felt at the beginning had entirely disappeared. A bird in the cylinder with me was leaning on one side, and very sick. It was my wish to continue the experiment till the bird died, but the steam-pump, conspiring, as I suspect, with the people who were watching me through glass peep-holes, would not work, and so I had to return to normal pressure.'
"So you see, Bill, it is the low tension of the oxygen and not the diminished pressure that produces the distress and suffering and even death."
"All this is very interesting, but our problem is not one of rarefied air; the atmosphere here is compressed."
"And, in compressed air," said Milton Rhodes, "it is the oxygen again that produces the symptoms. Subject a sparrow to a pressure of twenty atmospheres, and the bird is thrown into convulsions, stronger than those produced by tetanus or strychnine, convulsions which soon end in death. If pure oxygen is used, a pressure of only five atmospheres kills the sparrow. But, and mark this, if the air be deficient in oxygen, the pressure of twenty atmospheres does not produce even a tremor.
"So you see, Bill," Milton concluded, "we could descend to a very great depth in an atmosphere poor in oxygen."
"But how do we know that the atmosphere down there is poor in oxygen? It may be nothing of the kind. It may be saturated with it."
"Of course, we don't know. All we know is that we know nothing. And that reminds me of Socrates. That is what he said—that all he knew was that he didn't know anything. And Arcesilaus—Arcesilaus declared that Socrates didn't even know that much! However, hope is as cheap as despair. And, remember, here are our Hypogeans. They can ascend to our world, to a height of eight thousand feet above the level of the sea, and that, so far as we know, without suffering the slightest inconvenience."
"Something queer about that," was my comment.
"It is queer, Bill. However, we know that they can live in the (to them) rarefied air of our world: why, then, think that conditions down there, whether five miles down or fifty miles down, will prove fatal to us?"