"According to the law. But, as I remarked, there is something wrong with the law. 'Tis my belief that we shall be able to descend much deeper than ten and one half miles--that is, that the atmospheric pressure will permit us to do so." "That qualification," I told him, "is very apropos, for there is no telling what the inhabitants of this underground world will permit us to do or will do to us--bat-apes or ape-bats, humans, or both." "That, of course, is very true, Bill." "And," said I, "we won't need a manometer, or we won't need to ascertain the boiling-point of water, to know that the pressure is increasing. Our eardrums will make us painfully aware of that fact." "When that comes, swallow, Billy, swallow, and the pain will be no more." "Swallow?" "Swallow," Milton nodded. "Great Barmecide, swallow what?" "Swallow the pain, Bill. For look you. Deglutition opens the Eustachian tube. Some of the dense air enters the drum and counteracts the pressure on the outside of the membrane. You keep swallowing. The air in the drum becomes as dense as that outside; there is no pressure on the membrane now--or, rather, the pressures are in perfect equilibrium--and, presto and abracadabra, the pain is gone." "Who would have thunk it?" "A gink," said Rhodes, "going into compressed air had better think it, or do it without thinking it. He may have his eardrums burst in if he doesn't." "But why does the Eustachian tube open only when we swallow?" "To shut from the ear the sounds produced in the throat and mouth. If the tube were always open, our heads would be so many bedlams." "Wonderful Nature!" I exclaimed. "Oh, she does fairly well," admitted Milton Rhodes. "And I suppose," I said, "that the pain in the ears experienced by those who ascend high mountains is to be explained in the same way, only vice versa. They too ought to swallow." "Of course. At lofty heights, the dense air in the drum presses the membrane outwards. Swallowing permits the dense air to escape. One swallows until the pressure on the inside equals that of the rarefied outside air, and, hocus-pocus and presto, the pain has evaporated." "I hope," I said, "that all our difficulties will be as easily resolved." "Hey!" cried Milton. "What's the matter now?" "Stop _swallowing_ that water! We've got food sufficient for a week, but we haven't got water to last a week or anything like a week. Keep up that guzzling, and your canteen will be empty before sunset." "Sunset? Sweet Pluto! Sunrise, sunset or high noon, it's all the same here in Erebus." "You'll say that it's very different," dryly remarked Milton Rhodes, "if you find the fingers of Thirst at your throat." "Surely there is water in this place--somewhere." "Most certainly there is. But we don't know how far we are from that somewhere. And, until we get to it, our policy, Bill, must be one of watchful conservation."