The list is divisible into three chronological groups, each corresponding to a distinct period in Petty's life, and containing books that have a common provocation and common characteristics. The first group was produced in London after Petty had given up his arduous positions as physician to the army, surveyor of Ireland, and clerk of the Irish privy council, and before he was obliged to return to that island in order to defend the title of his lands in the Court of Claims. The two pamphlets of this group are directly due, respectively, to the fiscal discussions ensuing upon the Restoration and to the expensiveness of Charles II.'s first Dutch war. Their characteristic subject, accordingly, is taxation. But they contain such digressions to other topics as constitute them, for the student of economic theory, the most interesting of all Petty's writings.
The second group contains his best-known pamphlets, The Political Anatomy of Ireland and the Political Arithmetick. They were written in Ireland after his affairs there had settled into a satisfactory prosperity and he once more had leisure to exercise his mind upon those topics that he especially loved. The direct impulse to their writing came from Dr. Edward Chamberlayne's Present State of England, published in 1669,—a book, by the way, which seldom receives nowadays the attention that it deserves. In January, 1671, when a new edition of Chamberlayne's work was in prospect, Sir Joseph Williamson, later principal secretary of state, suggested to its author the addition of some matter regarding Ireland. Chamberlayne appealed for assistance to Petty, who chanced to be in London at the time; and Petty appears to have been so pleased with the idea that he decided to carry it out himself. Soon thereafter he began another pamphlet treating of England. To this he gave the title Political Arithmetick, which his work has made famous. This title, too, has the advantage of characterizing for us
