ESHS/HSS Annual Meeting

Revisiting Nineteenth-Century Visual Photometry: Instruments, Practices, and Reciprocal Influences

• In Event: Measurement and Instrumentation

English Abstract

In this presentation, I revisit visual photometry in the nineteenth century with new analytical perspectives, focusing on the observational instruments, procedures, and the attitudes underlying these practices in Britain, Germany, and the United States. I begin by examining the observational practices of John Herschel, often recognized as a pioneer of visual photometry but considered to have relied on very elementary apparatus and minimal data analysis. By reproducing the graphs he used to process his measurements, I reassess his role in the history of astronomical photometry. At the same time, I clarify how Gustav Fechner, who established the mathematical relationship between traditional star magnitudes and luminosity measured with new instruments through the Weber–Fechner law, used and evaluated Herschel’s observational data. I then turn to Edward Charles Pickering’s instruments and observational practices at the Harvard College Observatory, situating them in relation to contemporary programs at Potsdam and Oxford. Pickering’s approach involved the development of new instruments tailored to his needs and the routinization of observational procedures, providing a practical basis for comprehensive determination of photometric magnitudes. At Potsdam, Müller adopted the Zöllner photometer, with his approach differing in several respects from Pickering’s. I finally trace how Pickering’s later designs for observing fainter stars reflect influences from Müller’s ideas, the German photometer, and Oxford photometry by Charles Pritchard. Together, these instruments represent the culmination of nineteenth-century visual photometric efforts, shaped by the practices, reflections, and debates of astronomers who performed extensive visual observation.

Author

• Kaori Watanabe, University of Tokyo