"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?" "It does, most certainly; but there are little scrapers just in front of each runner which cut away the congealed oil to the merest fraction of an inch from the rail. These cutters must, by the train running between its upper and lower rails, always be just so far away, and no farther, from the rails." It seemed to Cobb that he could advance nothing but what this man had a ready explanation for its action or cause. It was, indeed, a most marvelous invention. Here he was traveling at the rate of two hundred and forty miles per hour, and scarcely felt the motion. "Where is the electricity for these powerful engines generated?" he inquired. "For the Central and Northern, as well as for the Pacific Pneumatic and Mountain lines, the dynamos are at the Shoshone Falls, in Idaho. These falls furnish an immense water-power, estimated at over 300,000 horse-power. The current is delivered at the station in great cables of peculiar construction, and well insulated." "Do you have any accidents on the roads? At such a rate of speed, an accident would be fraught with frightful consequences," Cobb continued. Rawolle smiled as he said: