Locke on measurement

•Overview of Locke's treatment of some long-standing problems in metrology in both his Essay and other sources.•Explanation of broader context of experimental philosophy and natural history for Locke's discussion of problems of measurement.•Detailed analysis of manuscript materials relating Locke's interest in metrology to his famous Essay.•Careful reconstruction of the development of Locke's proposed universal standard of measure for length over two decades.•New light on the impact of Isaac Newton on Locke and his Essay.

Like many virtuosi in his day, the English philosopher John Locke maintained an active interest in metrology. Yet for Locke, this was no mere hobby: questions concerning measurement were also implicated in his ongoing philosophical project to develop an account of human understanding. This paper follows Locke's treatment of four problems of measurement from the early Drafts A and B of the Essay concerning Human Understanding to the publication of this famous book and its aftermath. It traces Locke's attempt to develop a natural or universal standard for the measure of length, his attempts to grapple with the measurement of duration, as well as the problems of determining comparative measures for secondary qualities, and the problem of discriminating small differences in the conventional measures of his day. It is argued that the salient context for Locke's treatment of these problems is the new experimental philosophy and its method of experimental natural history.