in view he drew up a schedule for the improved registration of births, marriages, and deaths in Dublin, and tried in vain to secure royal approbation for an Irish statistical office. He saw clearly that government alone could ascertain the desired facts, and that governors would profit greatly thereby. "Until this be done," he adds, "trade will be too conjectural a work for any man to employ his thoughts about."[1] Meanwhile he made the best practicable use of such materials as were at hand, anatomizing Ireland with "only a commin Knife and a Clout, instead of the many more helps which such a Work requires." In one field alone was it possible to find a body of statistical data sufficiently extended and complete to warrant confidence in deductions properly made from it. For more than half a century the Company of Parish Clerks had kept weekly and annual records, in considerable detail, of births and deaths occurring in and about the city of London.[2] Upon these so-called "bills of mortality" Graunt had based the London Observations already mentioned. The most fertile field being thus pre-empted, Petty was obliged to cultivate ground whose arable spots were few and far separated. It is, indeed, surprising how slight his materials were. A few scattering bills from Dublin and Paris, hap-hazard returns of customs,—collections and the hearth tax, here and there a guess as to the area of a city, that is substantially all. Under these circumstances Petty had recourse, whenever he could not determine directly the number, weight, or measure of some fact under discussion, to that substitute for direct enumeration which distinguishes his Political Arithmetick from modern statistics. Statisticians enumerate: he multiplied. The value of his results varies according to the nature of the terms employed.
For example, in the absence of a census he was forced
