That iron should have been one of the last of the metals to come into general use, is partly accounted for by the circumstance that iron, though one of the most generally diffused of minerals, never presents itself in a natural state, except in meteorites; and that to recognise its ores, and then to separate the metal from its matrix, demands the exercise of no small amount of observation and invention. Persons unacquainted with minerals would be unable to discover the slightest affinity between the rough ironstone as brought up from the mine, and the iron or steel of commerce. To unpractised eyes they would seem to possess no properties in common, and it is only after subjecting the stone to severe processes of manufacture that usable metal can be obtained from it. The effectual reduction of the ore requires an intense heat, maintained by artificial methods, such as furnaces and blowing apparatus.[5] But it is principally in combination with other elements that iron is so valuable when compared with other metals. Thus, when combined with carbon, in varying proportions, substances are produced, so different, but each so valuable, that they might almost be regarded in the light of distinct metals,--such, for example, as cast-iron, and cast and bar steel; the various qualities of iron enabling it to be used for purposes so opposite as a steel pen and a railroad, the needle of a mariner's compass and an Armstrong gun, a surgeon's lancet and a steam engine, the mainspring of a watch and an iron ship, a pair of scissors and a Nasmyth hammer, a lady's earrings and a tubular bridge. The variety of purposes to which iron is thus capable of being applied, renders it of more use to mankind than all the other metals combined. Unlike iron, gold is found pure, and in an almost workable state; and at an early period in history, it seems to have been much more plentiful than iron or steel. But gold was unsuited for the purposes of tools, and would serve for neither a saw, a chisel, an axe, nor a sword; whilst tempered steel could answer all these purposes. Hence we find the early warlike nations making the backs of their swords of gold or copper, and economizing their steel to form the cutting edge. This is illustrated by many ancient Scandinavian weapons in the museum at Copenhagen, which indicate the greatest parsimony in the use of steel at a period when both gold and copper appear to have been comparatively abundant.