The New Stone Age seems to have passed gradually into the Age of Copper, because doubtless of a more or less accidental discovery when native copper was seen upon the ground, or when some copper ore was subjected to fire. The metal, by reason of its great durability, ductility, elasticity and strength, came to be used for many purposes--the first use being probably in weapons; for weapons were the main dependence of the people in their struggle against beasts. A great advance was made when bronze was discovered, with which weapons and tools of many kinds could be made that were harder than those of copper. Then the Age of Bronze succeeded the Age of Copper. One can hardly imagine that bronze was really invented; for it is difficult to see how, knowing the softness of copper and tin, any primeval man could have imagined a metal made from them much harder than either, and then proceeded to make it by mixing about seven parts of copper with one part of tin. The gradual improvement made in bronze implements, and the different kinds of bronze that later appeared (made by altering the proportions of tin and copper) were doubtless due more to constructive and engineering methods than to pure invention; but nevertheless a considerable amount of inventing must have been required; for one can rarely effect any important improvement in any weapon, instrument or tool, without first imagining the improvement, and then endeavoring to effect it. In fact, an overwhelming majority of the "inventions" for which patents are issued by our Patent Office, are for mere improvements over existing apparatus; and the bald fact that the thing accomplished is only such an improvement, instead of the creation of something different from everything else whatever, like the telephone or phonograph, does not debar the achievement from being classed as an invention. The pointed screw was merely an improvement over previous forms of screw, and yet it was an invention of high originality, novelty and importance. Obviously, improvements occupy various positions not only in importance and scope, but also in the relative degrees in which invention and construction were employed to bring them into being. It is held by some that no purely human act can possibly create anything really new, that "there is nothing new under the sun," and that therefore every so-called invention made by a man must be merely a novel arrangement of already existing objects.