"But the pressure. We can't go down very far into this steadily increasing pressure, increasing in a geometrical ratio whilst the depth increases only in an arithmetical one." "But," Milton said, "I showed you that there is something wrong with the law." "Then how do you know that we have reached a depth of twelve thousand feet and over, if the law breaks down?" "I don't believe that it has broken down yet. It will hold good for this slight descent which we have made. And, of course, if fact is found to coincide with theory, then our descent will be arrested at no great depth." "And," I said, "unless the discrepancy between fact and theory is a remarkable one, we will have no means of knowing whether the law has broken down or not. For it is impossible, in this world of utter darkness, to make anything like an accurate estimate of the descent made good." "We shall have no means of knowing, Bill, unless, as you say, truth and theory are remarkably divergent. Of course, in that case, we should not long remain unaware of the fact. Of the depth, then, we can not be certain; but the boiling-point of water will always give us the atmospheric pressure." "That isn't what is worrying me," I told him; "it is the pressure itself." "The pressure _itself_," Milton returned, "would produce no dire effects. It is not the diminution of pressure that produces the dreaded mountain sickness, as was clearly shown by Dr. Paul Bert. Of educated people, nine hundred and ninety-nine out of every thousand will tell you that the acceleration of the pulse as one ascends to lofty heights, the short, troubled breathing, the disordered vision, extreme weakness, nausea, vertigo, bleeding at nose and lungs in short, all the symptoms of the terrible _mal des montagnes_, are caused by the diminution of the atmospheric pressure. The average human being (such is their explanation) having a surface of about fifteen square feet, sustains an atmospheric pressure of thirty thousand pounds; at an elevation of eighteen thousand feet, the pressure is but one half of that; is it any wonder, then, that a man gets mountain sickness?" "Shades of ten thousand Gullivers," I exclaimed, "do you mean to say that those nine hundred and ninety-nine are wrong?" "Certainly they are wrong, so wrong as to cause Dr. Bert to write: "'It is amazing to find a theory so plainly at variance with elementary physical laws accepted by eminent men.'" "Well, well," was my sage remark, "I suppose the next thing on the programme will be the statement that it is not the fire that makes the pot boil; it is the heat; and that it is simply amazing to find a man who thinks that he has an iota of brains in his cranium entertaining the belief that it is the pot that boils."