"We will have to make a vertical descent of three and one half miles below the level of the sea—a vertical descent of near five miles from this spot where we stand, Bill—before we reach a pressure of even two atmospheres."
"The density then increases rapidly, doesn't it?"
"Oh, yes. Three and a half miles more, and we are under a pressure of four atmospheres, or about sixty pounds to the square inch. Three and a half miles farther down, or ten and one half miles in all below the level of the sea, and we have a pressure upon us of eight atmospheres. Fourteen miles, and it will be sixteen atmospheres. At thirty-five miles the air will have the density of water, at forty-eight miles it will be as dense as mercury, and at fifty miles we shall have it as dense as gold."
"That will do!" I told him. "You know that we can never get down that far."
"I have no idea how far we can go down, Bill."
"You know that we could never stand such pressures as those."
"I know that. But, as a matter of fact, I don't know what the pressures are at those depths. Nor does any other man know. What I said a moment ago is, of course, according to the law; but there is something wrong with the law, founded upon that of Mariotte—as any physicist will tell you."
"What's wrong with it?"
"At any rate, the law breaks down as one goes upward, and I have no doubt that it will be found to do so as one descends below the level of the sea. If the densities of the atmosphere decrease in a geometrical ratio as the distances from sea-level increase in an arithmetical ratio, then, at a distance of only one hundred miles up, we should have virtually a perfect vacuum. The rarity there would be absolutely inconceivable. For the atmospheric density at that height would be only one billioneth of what it is at the earth's surface."
"And what is the real density there?"