If one should take his stand for an hour upon London Bridge, perhaps the busiest bit of street in the world, and cast his eyes around intelligently to see what he can see, and begin also to classify the things coming under his vision, what might he report to himself and to others? Below the bridge in what is called the "Pool," which was dredged out for that very purpose by the ancient Romans, there lie at anchor or move coming and going many merchant-ships of all nations, carrying out and bringing in to an immense amount in the whole aggregate tangible articles of all kinds to and from the remote as well as the near nations of the earth. All this movement of visible goods, home and foreign, is in the interest and under the impulse of Buying and Selling. The foreign goods come in simply to buy, that is, to pay for, the domestic goods taken away; and these latter go out in effect even if not in appearance to buy, that is, to pay for, the foreign goods coming in. At the same hour the bridge itself is covered with land-vehicles of every sort moving in both directions, loaded with salable articles of every description; artisans of every name are coming and going; merchants of many nationalities step within the field of view; and porters and servants and errand-boys are running to and fro, all in some direct relation to the sale or purchase of those visible and tangible things called in Political Economy _Commodities_. Moreover, vast warehouses built in the sole interest of trade on both sides the river above and below the bridge, built to receive and to store for a time till their ultimate consumers are found, some of these thousand things bought and sold among men, lift their roofs towards heaven in plain sight. Doubtless some few persons, like our observer himself, may be on the spot for pleasure or instruction, but for the most part, all that he can see, the persons, the things, the buildings, even the bridge itself, are where they are in the interest of _Sales_ of some sort, mostly of Commodities. What is thus true of a single point in London is true in a degree of every other part of London, of every part of Paris and of Berlin, and in its measure of every other city and village and hamlet in the whole world. Wherever there is a street there is some exchange of commodities upon it, and wherever there is a market there are buyers and sellers of commodities.