"Man, with respect to all those matters, is more a creature of consistency than he is aware, or than governments would wish him to believe. All the great laws of society are laws of nature. Those of trade and commerce, whether with respect to the intercourse of individuals or of nations, are laws of mutual and reciprocal interest. They are followed and obeyed, because it is the interest of the parties so to do, and not on account of any formal laws their governments may impose or interpose."