I will begin by noticing that the present age has settled a question which caused much debate, and which puzzled Grote (ii. 142) and a host of others half a century ago, before phosphor-bronze was invented. This was the art of hardening (not tempering) copper and its alloys. All knew that these metals had been used, in cutting the most refractory substances,[156] granite, syenite, porphyry, basalt, and perhaps diorite,[157] by the ancient Egyptians, Assyrians, Trojans, and Peruvians. But none knew the process, and some cut the knot by questioning its reality. When you cannot explain, deny—is a rule with many scientists. The difficulty was removed by the Uchatius-gun,[158] long reported to be of ‘steel-bronze,’[159] but simply of common bronze hardened by compression. At the Anthropological Congress of Laibach[160] (July 27–29, 1878), Gundaker Graf Wurmbrandt, of Pettau, exhibited sundry castings, two spear-heads and a leaf-shaped blade of bright bronze (Dowris copper) adorned with spirals to imitate the old weapons. They were so indurated by compression that they cut the common metal. 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.