In the 1850s humans arrived at the mass production of steel, an alloy of iron, carbon, and manganese having a tensile strength of 50,000 p.s.i. as well as a compression-resisting capability of 50.000 p.s.i. Steel has the same compression-resistance capability as masonry, but it also has a thousand times greater tensile capability than masonry and five times the tensile or compressive strength of wood. Steel brought mankind a structural-tension capability to match stone’s previous millions of years of exclusive compressional supremacy. With far higher tensile strength per weight than wood, steel made possible even more powerful watertight, air-containing vessels than did wood, even though steel by itself does not float.