The youths paused at this point to look at the drawings which showed the design for supporting the cradle on its carriage. Fred observed that the axle of each wheel was independent, and that there was a pair of springs above each and every wheel. He asked Doctor Bronson why it was so many springs were needed, as it was evident that with twelve hundred wheels there would be twenty-four hundred springs.
"I suppose," was the reply, "that it is to facilitate the change of the carriage from a level to a grade, or vice versâ. In going from an up grade to a level there would be a greater pressure at the ends than in the centre, and the same would be the case in going from a level to a down grade. The springs are intended to regulate this; the railway is intended to form an upward incline from each end towards the centre, where there will be a level of several miles."
Frank asked how fast the train, if train it could be called, was expected to run in making the transit of the isthmus with a ship.
"From eight to ten miles an hour," replied the Doctor. "Captain Eads proposed not to keep a vessel more than twelve hours out of the water, and he thought it quite likely the time might be reduced to ten hours."
Then the youths looked at the map and studied out the course of the proposed ship-railway. Frank slowly dictated while Fred jotted down the names of the places mentioned.
"The bar at the mouth of the river must be dredged out so as to admit ships, which will then find plenty of water up to a point called Ceiba Bonita, on the Uspanapan River, which runs into the Coatzacoalcos just below Minatitlan. There the ship-railway will begin, and it runs in a straight line to the mountains, where there is a depression only 650 feet high. In fact there are two of these depressions, and either of them may be taken. These are the passes of Chivela and Tarifa. By the former the railway may run to the town of Tehuantepec, and there make a bend by turn-table, and continue to the Pacific Ocean; and by the latter pass it may go to Salinas Cruz, which lies on a lagoon, where a harbor must be dredged out."
"And how much will be the cost of this great work?" one of the youths asked.