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Again, at the Anthropological Congress of Salzburg (August 8, 1881), Dr. Otto Tischler, of Prussian Königsberg, repeated the old experiment, showing how soft copper and bronze could be hardened by the opus mallei (simple hammering). Moreover his metal thus compressed could cut and work the common soft kinds without the aid of iron or steel. He exhibited two bronze plates in which various patterns had been punched by bronze dies. The hammering, rolling, beating, and pressing of copper for the purpose of hardening are well known to modern, and doubtless were to ancient workmen. The degree of compression applied is the feature of the discovery, or rather re-discovery.[161]

It may be doubted whether old Egypt and Peru knew our actual process of hydraulic pressure, whose simplest form is the waterfall. But they applied the force in its most efficient form. The hardest stones were grooved to make obelisks; the cuts were filled with wedges of kiln-dried wood, generally sycomore; and the latter, when saturated with water, split the stone by their expansion. And we can hardly deny that a people who could transport masses weighing 887 tons[162] over a broken country, from El-Suwan (Assouan) to Thebes, a distance of 130 miles, would also be capable of effecting mechanical compression to a high degree.