Sir William Petty on the Causes and Consequences of Urban Growth

Abstract

If modern economic science is built on the twin foundations offactual investigation and deductive reasoning from clearly stated premises, Marx's characterization of Sir William Petty (1623-87) as the founder of economics is well deserved. His Political Arithmetick was a pathbreaking effort the art of reasoning byfigures upon things relating to government. Although Petty's primary concern lay analyzing problems of taxation, money, international trade, and national income, he was also interested demographic processes and their relation to economic phenomena. The passage reproduced below from pp. 26-40 of his An Essay Concerning the Multiplication of Mankind Together with another Essay Political Arithmetick, Concerning the Growth of the City of London with the Measures, Periods, Causes, and thereof. 1682. (London, 1698) is an appealing display of that interest. The first part of this essay is devoted to an astute ifflawed estimation of the size and rate of growth of the population of the globe, of England, and of the City of London. Petty set the global population at 320 million (about half of its actual level) and estimated that it was increasing at a geometric progression with a doubling time of 360 years. Thus, he reasoned, world population within the next 2000 years so increase as to give one Headfor every two Acres of Land the Habitable part of the Earth. At that density (with a total population of some 10 billion), Petty expected Wars and great Slaughter &c. The population of the City of London he estimated as 670,000, doubling every 40 years. Both of these figures (both overestimates) were derived from a time series of burials, taken from Graunt's celebrated Natural and political observations made upon the Bills of Mortality (1662), a series that Petty extended to 1682. (Burials in such Years as were neither remarkable for extraordinary Healthfulness or Sickliness tended to be doubling every 40 years, Petty observed, and he assumed that such years there was one death for every 30 persons alive.) Since the population of England and Wales (like that of the globe) grew much more slowly than that of London, Petty reasoned that London's growth would come to a halt by Anno 1800, when it will be eight times more than now, with above 4 millions. What are the Causes and Consequences of London's growth? This is the subject Petty addresses the excerpt reproduced below. Characteristically,