"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?" "No man knows or can know," replied Rhodes, "until he goes up there to see. But meteors, rendered incandescent by the resistance they encounter, show that a state of things exists at that high altitude very different from the one that would be found there if our formulae were correct and our theories were valid. And so, I have no doubt, we shall find it down in Drome. "Formulae are very well in their place," he went on, "but we should never forget, Bill, that they are often builded on mere assumption and that a theory is only a theory until experiment (or experience) has shown us that it is a fact. And that reminds me: do you know what Percival Lowell says about formulae?" I said that I didn't. "'Formulae,' says the great astronomer, 'are the anaesthetics of thought.' "I commend that very highly," Milton Rhodes added, "to our fiction editors and our writers of short stories." "But--" "But me no buts, Bill," said Milton. "And what do your scientists know about the interior of this old earth that we inhabit, anyway? Forsooth, but very little, Billy, me lad. Why they don't even know what a volcano is. One can't make a journey into the interior of the earth on a scratch-pad and a lead-pencil, or, if he does, we may be pardoned if we do not give implicit credence to all that he chooses to tell us when he comes back. For instance, one of these armchair Columbuses (he made the journey in a machine called d^2y by dx^2 and came out in China) says that he found the interior in a state of igneous fluidity. And another? Why, he tells us that the whole earth is as rigid as steel, that it is solid to the very core." "It seems," said I, "to be a case of "'Great contest follows, and much learned dust Involves the combatants; each claiming truth, And truth disclaiming both.'" "The truth, in this case, is not yet known, of course," replied Milton Rhodes, "though I trust that you and I, Bill, are fated to learn it--some of it, I should say." He smiled a queer, wan smile.