ture of money (218). A conspicuous case of the fortune of a city being determined by natural location is pointed out in London (27 and 28). It will always be the greatest city in England, because the Thames is the most commodious river in the island, and because London is placed on the most commodious part of the Thames. The situation of Ireland proves that it is naturally adapted to trade with America, for in the southwestern part of that island the most commodious ports are found (354). Petty believed that these natural differences might be expressed in exact language. In addition to comparative meteorological observations, he proposed that the natural advantages of different soils should be mathematically estimated by agricultural experiments (335).
The main factor in the creation of wealth is labor. Without it natural advantages are insufficient, and by it natural disadvantages can be overcome. Ireland, he points out, has many natural advantages. Why is it such an undeveloped country? He answers by declaring that the Irish themselves "are unprepared for trade" (354), because their necessities are few. They want no foreign commodities but tobacco. Where there is no internal trade, there is no incentive to labor. "Husbandmen, seamen, soldiers, artizans and merchants are the very pillars of any commonwealth; all the other professions do rise out of the infirmities and miscarriages of these" (223). In these different forms labor has not the same value. More is to be gained by manufactures than by husbandry, and by merchandise than by manufactures (220).
