“Even were we to use a smaller wheel to decrease the centrifugal force, we would have to increase the number of revolutions, so there would be no gain in so doing. Our trains run upon two peculiarly constructed rails, and the runners are flanged to exactly fit the rail. There is, in addition, on either side of the tunnel, another rail of similar shape, while upon the upper part are two more. The car has runners for all of these rails, and the position of them is such that the car cannot jump the track, or swing or sway from side to side. It travels as if in a groove, and the little runners, separate from one another, conform to the curves of the tunnel.”
“It must take powerful engines to exhaust the air from such a long tunnel, does it not?”
“Yes, very powerful ones. But what is different from any other mode of propulsion, the same engine can do as much service for a line 2,000 miles long as for one of 200 miles in length, rate of speed being the same. The reason for stations at intervals of about 500 miles, is because more trains can be kept in motion on medium short lines than on very long ones. There are at Salt Lake, at the receiving end of this line, fifteen engines of 5,000 horse-power each; ten at work all the time, with five in reserve.”
“A pretty strong set of engines for a single railroad, I would say; and a costly motive power, too.”
“Not so costly as you would think,” he returned. “If you take into consideration that these engines are worked by electricity, and not by steam, and that the electricity is furnished by water-power, you will perceive that they can be worked quite cheaply.”
“Give me some of the statistics, please,” said Cobb.
“Certainly. The tunnel is twelve feet in diameter, which gives it a superficial area of 17,712 square inches. Now, at a pressure of one pound to the square inch, a train has a pushing force at its end of the same number of pounds. A train weighs 50,000 pounds. The heaviest grades on the line are some of two hundred feet to the mile. The power required to push this train up such grades is 2,000 pounds, for the matter of friction is not taken into consideration, being, by our arrangements, reduced to the minimum. Thus the pressure in the tunnel is always sufficient to move eight trains. If a train moves four miles in a minute, then the volume of air in the tunnel to be displaced is equivalent to the area multiplied by the length, which gives 2,600,000 cubic feet; but, under a pressure of one pound, this volume becomes 3,000,000. The pumps at each station are ten in number, each of thirty feet diameter by ten-foot stroke, with a volume for each of 7,060 cubic feet. These pumps make thirty strokes per minute, which is equivalent to sixty single strokes. Thus the volume of air displaced by the pumps is 7,060 × 60 × 10 = 4,236,000 cubic feet, an amount far in excess of that required.”
“Then, judging from your remarks, there is practically no limit to the speed which can be obtained by this method of propulsion?”
“On the contrary,” Rawolle returned, “the limit is reached when the friction on the runners generates such an amount of heat that they begin to disintegrate. At three hundred miles per hour they become very hot. As it is, we have to use a very peculiar kind of alloy for runners, and during all the time of running, keep a stream of oil flowing just in front of each runner.”
“But,” asked Cobb, “does not this oil congeal upon the rail in cold weather?”