Petty's instruments: the Down Survey, territorial natural history and the birth of statistics

William Petty's work has usually been regarded as an epistemic break in the history of statistical and politico-economic thought. In this paper, I argue that Petty's statistical notions stemmed from the natural-historical techniques he originally implemented to manage the Down Survey. Following Bacon, who viewed the description of trades as a paramount branch of natural history, Petty approached the art of surveying itself as an object of natural-historical analysis. He partitioned the surveying work into individual tasks and implemented a meticulous division of labour, employing hundreds of disbanded soldiers as surveyors and using questionnaires to calibrate the responses of his 'instruments', as he called his specialized workers. By borrowing these methods from natural history to organize surveying work, Petty was able to conceptualize Ireland as a political body defined by tables of aggregate data. I then compare the Down Survey with John Graunt's observations on the bills of mortality to show that both are representative of a particular style of natural history, aimed at describing the natural and political state of a circumscribed territory. I close by considering other manifestations of 'territorial natural history', indicating a continuity between this research tradition and the appearance of statistics in the British Isles.