"And in the midst of it is a cave which is turned the way of hell. And therein dwells Scylla, whining for prey: her cry, indeed, is no louder than that of a newly-born whelp: but she herself is an awful thing--nor can any creature see her face and be glad; no, though it were a god that rose against her. For she has twelve feet, all fore-feet, and six necks, and terrible heads on them; and each has three rows of teeth, full of black death. "But the opposite rock is lower than this, though but a bow-shot distant; and upon it there is a great fig-tree, full of leaves; and under it the terrible Charybdis sucks it down, and thrice casts it up again; be not thou there when she sucks down, for Neptune himself could not save thee." The reader will find the meaning of these types gradually elicited as we proceed. This disease of desire having especial relation to the great art of Exchange, or Commerce, we must, in order to complete our code of first principles, shortly state the nature and limits of that art. As the currency conveys right of choice out of many things in exchange for one, so Commerce is the agency by which the power of choice is obtained; and countries producing only timber can obtain for their timber silk and gold; or, naturally producing only jewels and frankincense, can obtain for them cattle and corn. In this function commerce is of more importance to a country in proportion to the limitations of its products and the restlessness of its fancy;--generally of greater importance towards Northern latitudes.