The Wealth of Nations by Part 2 Chapter 2 Page 51

But as that coin will not be allowed to lie idle, it must, in one shape or another, be sent abroad, in order to find that profitable employment which it cannot find at home; and this continual exportation of gold and silver, by enhancing the difficulty, must necessarily enhance still further the expense of the bank, in finding new gold and silver in order to replenish those coffers, which empty themselves so very rapidly. Such a company, therefore, must, in proportion to this forced increase of their business, increase the second article of their expense still more than the first.

Let us suppose that all the paper of a particular bank, which the circulation of the country can easily absorb and employ, amounts exactly to forty thousand pounds; and that for answering occasional demands,