JAMES BUCHANAN EADS IS KNOWN AS THE GREAT ENGI neer of the Mississippi. Born in Indiana in 1820, he was just 22 when he persuaded a St. Louis shipbuilding firm to build a new kind of “submarine” vessel to recover cargo from sunken Mississippi steamboats and with it launched a salvage business so successful that he contemplated retiring at 37. During the Civil War he built ironclad gunboats to defend the river. After that he crossed it with America’s first major bridge with steel arches, the Eads Bridge, at St. Louis. And in the late 187Os he devised jetties at the mouth of the river that permanently opened it to oceangoing vessels. But his biggest idea had nothing to do with the Mississippi.

In May 1879 a congress was held in Paris to devise a plan for linking the Atlantic and Pacific Oceans. At it, Ferdinand de Lesseps, the French diplomat who had overseen the construction of the Suez Canal, proposed a Panama canal. Just a month after the congress, Eads wrote letters to two New York newspapers suggesting a very different way to connect the oceans. He wanted to build a gargantuan railway that would transport whole ships across 134 miles of land between the oceans at the Isthmus of Tehuantepec, the narrowest part of Mexico (where the total distance between the east and west coasts would be 2,000 miles shorter than a trip across Panama).

His idea was to raise the ships onto 350-foot-long flatcars. At either end of the isthmus a 450-foot-long submerged-pontoon dry dock would be loaded with a flatcar; the car would carry an adjustable cradle with hydraulic rams to make it conform to the shape of a ship’s hull. Once the car and its cradle were on the pontoon, a ship would sail into position above them. Then water would be pumped out of the dry dock to lift it up to the level of the tracks, whereupon three outsized locomotives would hitch up and pull the car forward. They would ride on six parallel rails spanning 72 feet. Since the car would be too long to negotiate curves with a radius of less than 20 miles, huge turntables would be placed at every change in direction. Once a train was across the isthmus, the process by which the ship had left the water would be reversed.

Eads was convinced this was the most efficient way to link the oceans. In an address to the San Francisco Chamber of Commerce in 1880 he said, “I declare to you, First , that a ship railway can be constructed at one-half of the cost of a canal with locks, and in one-half the time. Second , that when completed, the railway can be maintained and operated at a cost not exceeding that of a canal. Third , that our largest vessels with their cargoes can be safely carried from ocean to ocean in one-half the time required for passage through the canal.”

He told a congressional committee that he could get it built for a quarter of the price Lesseps was overoptimistically predicting for his canal. When the committee didn’t give a goahead, he said he would undertake it at his own expense if the government guaranteed a dividend of 6 percent on the stock he sold. Then in 1881 Lesseps’s canal got started.

Eads spent the next six years trying to get Congress to back his scheme, showing off a 30-foot-long working model with a 6-foot ship, which he had built for $10,000 of his own money. The reaction was mixed. In the winter of 1887 he was vacationing in the Bahamas when he received word that the Senate had finally approved the plan. But on March 8 that year he died, unaware that opponents in the House had just blocked it.

His grand scheme passed away with him, an audacious plan that just might have succeeded. In 1889 the French company building the canal went bankrupt, plagued by soaring costs, financial scandals, and ruinous disease at the work site. The United States finished the canal in 1914, 33 years after Lesseps had started it, at a cost of $352,000,000.

Not only is Eads’s alternative almost universally forgotten today, but the working model he built has long been lost too, and no photographs of it are even known to exist. Yet surely it would have been one of the engineering wonders of the world.