The discovery of bronze marked an important epoch in the progress of human development; and it would be difficult to estimate its full value as an element in the economic and social conditions of primitive man and early civilizations. In Ireland as elsewhere, owing to its advantages, bronze in time came into general use in the manufacture of weapons, domestic implements, and articles of personal adornment. These passed through various stages of development; and the use of bronze, as the general material for all such articles, became in time very widespread. The percentage of tin in bronze varies, and the proportion does not appear to be absolutely fixed. About 10 per cent. seems to have been the average for the best bronze. Some Irish bronze implements yielded, on analysis, 13·88 per cent.; the Mycenæan bronze which Schliemann had examined gave 13 per cent. of tin; and some bronze from Hissarlik gave 4 to 6 per cent. The number of moulds discovered for various weapons shows that smelting was practised in Ireland; but, like the mining, it is difficult, if not impossible, to ascertain the exact method of working, and the extent to which it was carried on.[93] Archæological opinion is divided as to the origin of bronze. It has been variously attributed to the high table-land of Central Asia, to India, to Siberia, and to the original inhabitants of the lower Euphrates valley, while some writers claim for it an Etruscan origin. Its antiquity is, however, great; Dr. Flinders Petrie found celts in the tombs of Medum in Egypt, structures which he considers lead back to the Third Dynasty; in the Fourth Dynasty, bronze came into general use.[94] It was characteristic of the whole of the Mycenæan civilization, and prevailed throughout the Homeric period, though iron was then known. Bronze spread to Europe from south to north along the established trade routes; and the theory, once held, that a Bronze Age developed independently among the rude races of Northern Europe is no longer accepted. The discovery of well-wrought weapons in early graves shows that the inhabitants of the British Isles first knew bronze, in its best form, as a foreign introduction, before they manufactured the metal for themselves. Bronze was, in time, superseded by iron; but not until the discovery was made of tempering or hardening it by plunging the hot metal into cold water. Iron was used by the Egyptians in the period from 3800 B.C. to 3000 B.C.; in depicting weapons or tools, it was the custom to paint iron blue or black--the colour by which it was known--and this is seen in the paintings which have been discovered of the time. ‘Iron,’ says Dr. Budge, ‘was certainly known to the Egyptians as early as the Fifth Dynasty; and, from the fact that iron plays a great part in ancient Egyptian myths, it is probable that it was known by them at a far earlier period.’[95] Metal tools of the best kind were known in Egypt at an early date. Dr. Petrie shows that drilling,