From Postal Scale to Psychological Apparatus A History of Experimental Psychology Through the Reconstruction of Peirce and Jastrow’s “On Small Differences of Sensation” (1885)

This paper describes our reconstruction of the apparatus used in C.S. Peirce and Joseph Jastrow’s 1885 psychophysical experiment, “On Small Differences of Sensation” and how it relates to persistent questions in scientific theories of measurement. We situate Peirce and Jastrow’s work in the broader context of nineteenth-century discussions about the status of psychology as a science and emphasize the role of measurement and experiment in determining that status. Through our re-enactment of the experiment, we analyze the experiment’s methodology, which features blinding, randomization, noise control, and a technology for data recording. Our claims are illustrated by images of historical and reconstructed apparatuses, as well as graphs of the data collected in our reproduction. Our findings exemplify the relevance of history of psychology for contemporary philosophy of science and theories of measurement, and defend experimental reconstructions as a particularly fertile method of inquiry in the history of psychophysical sciences.