Their quantity, in every particular country, seems to depend upon two different circumstances; first, upon its power of purchasing, upon the state of its industry, upon the annual produce of its land and labour, in consequence of which it can afford to employ a greater or a smaller quantity of labour and subsistence, in bringing or purchasing such superfluities as gold and silver, either from its own mines, or from those of other countries; and, secondly, upon the fertility or barrenness of the mines which may happen at any particular time to supply the commercial world with those metals.