How do you lift a 50,000 ton weight up to a level twenty or thirty feet high? Let me tell you about one way of doing it.

This is the weight of a giant ocean transport vessel steaming up the St. Lawrence Seaway. It approaches the Dwight D. Eisenhower Lock, and there a wall of steel looms before it. But the wall opens and the ship enters. Then the wall closes and water flows in. Gradually the ship is lifted - un…