If then it can be proved that throughout the area in which those weight standards arose from which all the known systems of the ancient, mediaeval, and modern world were derived, the same gold-unit is found everywhere, and that wherever evidence is to hand, this unit is regarded as equal in value to a cow or ox, the truth of our hypothesis will have been demonstrated. For it would be impossible that such an occurrence should be a mere coincidence if found repeated in different areas. Furthermore, if it can be shown that in cases at a comparatively late historical period peoples who were borrowing a ready-made metallic system from more civilized neighbours, have found it impossible to do so without adjusting or equating such metallic standard to their own unit of barter, we may infer _a fortiori_ that it would have been impossible for any people to have framed a metallic unit for the first time for themselves without any reference to the unit of barter. But as we have already proved that the unit of barter is in every case earlier in existence than even the very knowledge of the precious metals, it follows irresistibly that the metallic unit is based on the unit of barter. We have also given reasons for believing that gold was the first of the metals known to primitive man, but as yet we have not proved that the metals are the first objects to be weighed. If this can be proved, and if furthermore it can be proved that before silver or copper or iron were yet weighed, gold has been weighed by that standard, which we find universal in later times, we have still more closely narrowed down our argument and put it beyond all reasonable doubt that weighing was first invented for traffic in gold, and since the weight-unit of gold is found regularly to be the value of a cow or ox, the conclusion must follow that the unit of weight is ultimately derived from the value in gold of a cow.