"Our trains have been averaging about fifty tons, and for that weight we have found that a pound pressure is quite sufficient. Now, taking the tunnel's length as four thousand miles (of course it is not that long, but round figures are most convenient) and the tube width eleven and one quarter feet each and working this out we have 3,020,000 cubic feet of free air per minute or 2,904,000 cubic feet of compressed air, which would use about 70,000 horse power on the air compressor." "But isn't the speed rather dizzy?" "Not any more dizzy, Bob, than those old fashioned money-carrying machines that the department stores used to use--that is in comparison to size. The average speed is about 360 feet a second. Of course, the train is allowed to slow down toward the end of its run, even before it hits the braking machinery beyond the gate." "But how much pressure did you say would be put on the back of the diaphragm--I remember that each car has a flat disc on the back that fits fairly tightly to the tube ..." "The pressure on the back is less than seven tons. However, the disc does not fit tight. There are several leaks. For instance, the cars are as you know, run on the principle of the monorail with a guiding rail on each side. The grooves for the rails with their three rollers are in each car. There is a slight leakage of air here." "You used the turbo type of blower, didn't you?" "Had to because of the noise. We put some silencing devices on that and yet we could not kill all of the racket. However a new invention has come up that we will make use of soon now." * * * * * "But I can't understand, Dutch, why you seemed so put out when I announced my intention of going to Europe via the Tube. Why, I can remember the day when that would have tickled you to death." "You followed the digging of the Tube, didn't you?" "Yes, of course." "You remember the volcano and lava seams?" "Yes." "Well, I do not believe that the crack was a pressure crevice. If it had been, we were far enough below the ocean floor to have partly relieved the situation by the unusually solid building of the Tube. The tremendous shell of this new type of specially hardened metal--" "And the rich concrete that was used as filling! That was one job no one slipped up on. I remember how you watched it--" "Yet the crack has widened, Bob, since the Tube was completed." "How can you be certain?" "By the amount of water coming through the drain pipes." "But you said that once more it was stationary." "Yes, and that is the very thing that proves, I believe, the nature of the crack." "I don't follow you." "Why it isn't a crack at all, Bob. It is an earthquake fault." "Good heavens, you don't mean--"