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only the most conspicuous and clumsy firstfruits of a far more extensive process. Technical knowledge and skill were developing with an extraordinary rapidity, and to an extraordinary extent measured by the progress of any previous age. Far less conspicuous at first in everyday life, but finally far more important, was the extension of man's power over various structural materials. Before the middle of the eighteenth century iron was reduced from its ores by means of wood-charcoal, was handled in small pieces, and hammered and wrought into shape. It was material for a craftsman. Quality and treatment were enormously dependent upon the experience and sagacity of the individual iron worker. The largest masses of iron that could be dealt with under those conditions amounted at most (in the sixteenth century) to two or three tons. (There was a very definite upward limit, therefore, to the size of cannon.) The blast furnace arose in the eighteenth century, and developed with the use of coke. Not before the eighteenth century do we find rolled sheet iron (1728) and rolled rods and bars (1783). Nasmyth's steam hammer came as late as 1838. The ancient world, because of its metallurgical inferiority, could not use steam. The steam engine, even the primitive pumping engine, could not develop before sheet iron was available. The early engines seem to the modern eye very pitiful and clumsy bits of ironmongery, but they were the utmost that the metallurgical science of the time could do. As late as 1856 came the Bessemer process, and presently (1864) the open-hearth process, in which steel and every sort of iron could be melted, purified, and cast in a manner and upon a scale hitherto unheard of. To-day in the electric furnace one may see tons of incandescent steel swirling about like boiling milk in a saucepan. Nothing in the previous practical advances of mankind is comparable in its consequences to the complete mastery over enormous masses of steel and iron and over their texture and quality which man has now achieved. The railways and early engines of all sorts were the mere first triumphs of the new metallurgical methods. Presently came ships of iron and steel, vast bridges, and a new way of building with steel upon a gigantic scale. Men realized too late that they had planned their railways with far too timid a gauge, that they could have organized their