The account of these circumstances, with the discussion of the errors of this system, form the matter of the third and fourth books. * * * * * Political Economy is, of all sciences, that which affords most room for prejudices, and in which they are most liable to become deeply rooted. The desire of improving our condition, that universal principle, which continually acts upon every member of the community, is ever directing the thoughts of each individual to the means of increasing his private fortune. But should this individual ever chance to raise his views to the management of the public money, he would naturally be led to reason from analogy, and apply to the general interest of his country those principles which reflection and experience have led him to regard as the best guides in the conduct of his own private affairs. Thus, from attending to the fact, that money constitutes a part of the productive stock in the fortune of an individual, and that his fortune increases in proportion to the increase of this article, there arises that erroneous opinion so generally received, that money is a constituent part of national wealth, and that a country becomes rich, in proportion as it receives money from those countries with which it has commercial connections. Merchants who have been accustomed to retire each night to their desks, to count, with eagerness, the quantity of currency, or of good debts, which their day's sale has produced, calculating their profits only by this result, and confident that such a calculation has never deceived them, are naturally led to think that the affairs of the nation must follow the same rule; and they have been strengthened in this opinion by that unshaken confidence which a long and never-failing experience, that has been the source of wealth and prosperity, inspires. Hence those extravagant opinions respecting the advantages and profits of foreign commerce, and the importance of money; hence those absurd calculations that have been made regarding what is termed the balance of trade, the thermometer of public prosperity; hence those systems of regulations, and those oppressive monopolies, which are resorted to for the purpose of making one side of the balance preponderate; hence, too, those bloody and destructive wars, which have raged in both hemispheres, from the period in which the road to the Indies, and to the new world, became familiar to European nations.