Friday

In the 19^th century, experimental research continued to expand both in quantity and quality, to ever more fields and with ever more instruments, sophistication, and sometimes precision. At the same time, methods of reasoning from experiment found more reflections than before, both by philosophers and by practitioners themselves, and in different domains such as optics, electromagnetism, (organic) chemistry, or physiology. Both in practice and in reflection, major ideals of 18^th ct. considerations were further developed, such as the ideal of “reduction” towards (empirical) principles or the analysis towards (hidden) causes. Experimental control played out on many levels, with the overall aim to establish solidity of the resulting knowledge claims. Considerations reached from ways of securing individual experimental results to using them as support for explanations, from identifying ‘simple’ cases among phenomena to establishing empirical laws, from calibration methods of instruments to ways of assigning limits of detectability. In my talk, I will track and analyze some of these strands, relying on different types of publications, from experimental handbooks to philosophical treatises. 

Brownian movement is the completely irregular movement of microscopic particles of solid matter when suspended in liquids.Although it was known for the most part of the nineteenth century it was only at the end of that century that the importance of the phenomenon for the kinetic-molecular theory of matter was recognized. Historians of science have expressed both surprise and lament about the fact that Brownian movement did not play a role in the early development and justification of the kinetic theory of gases. If the liquid's molecular motion was identified from the beginning as the proper cause of the phenomenon,some of the main philosophical and scientific objections raised against the early kinetic theory of gases could have been answered. Related to this received historiographical position is the claim that most of the nineteenth century experimental investigations on the cause of Brownian movement were of a somewhat lower scientific rigor than the later experiments that successfully established molecular motion as the unique cause of the phenomenon (Brush 1968; Nye 1972; Maiocchi 1990)

I present the complexities of the nineteenth century investigations on the cause of Brownian movement and make sense of its late connection with the kinetic-molecular theory of matter. I argue that there was actually extensive and rigorous experimental work done on the phenomenon of Brownian movement throughout the course of the nineteenth century. Most investigators were fully aware of the methodological standards of their time and spent much effort to make their work adhere to these standards. There were two main methodological strategies they employed: 

1. The first was the inductive strategy of varying the experimental parameters to identify causal relations. This is the traditional Baconian strategy of varying the circumstances, which was codified in a more rigorous form during the nineteenth century in the methodological works of John Herschel and John S. Mill. Its underlying rationale was that all the circumstances that couldbe varied or excluded without affecting the phenomenon under investigation, could not be causes of the phenomenon. On the other hand, all the circumstances whose exclusion or variation had an influence on the phenomenon under investigation were considered to be causal factors.                                                                                                                   
2. The second was the hypothetico-deductive strategy (or the Method of Hypothesis--as it was called at the time), which made a dynamical re-emergence during the course of the nineteenth century as the proper strategy for validating hypotheses regarding unobservables. This strategy was mostly exemplified in William Whewell's notion of the Consilience of Inductions. Its underlying rationale was that the ability of a hypothesis (about unobservables) to explain a variety of experimental facts--especially facts that played no role in the initial hypothesis formation--indicated the validity of the hypothesis.

Each strategy had its own limitations when investigating the cause of Brownian movement. It was only the fruitful combination of these (prima facie) antithetical strategies that led, at the end of the nineteenth century, to the recognition of molecular motion as the most probable cause of Brownian movement.

Psychical research has proven an incredibly fruitful ground for methodological debates, both from historical actors and modern interpreters (Noakes 2014; Gooday 2004; Bensaude-Vincent & Blondel, 2001; Mauskopf & McVaugh 1980). Crucial for the possibility of a debate over psychical phenomena was the methodological commitment to a “careful examination of all kind of phenomena” (Peirce 1883/4). However, how was this commitment to be carried out in practice? And under which understanding of evidence? Starting from the controversy between Charles S. Peirce, the North-American pragmatist, and Edmund Gurney, co-founder of the Society for Psychical Research (British division), over the evidential weight of testimonies collected in Phantasms of the Living (Gurney, Myers and Podmore, 1886), I examine the parallel development of statistical and analytical tools to control for “spontaneous” phenomena and to assess their relevance.  

Philosopher Carl Stumpf carried out extensive studies of language sounds in the 1910s. The apparatus he constructed for this allowed for the comparison of observers with full information on the experimental process and experimental subjects without previous knowledge of the sounds they were supposed to judge. My paper will trace the way towards this research in three steps. I’ll start from the notion of Sachverhalt (state of affairs) that Stumpf develops in his logic as developed during the decade preceding these experiments. While grounding in juridical terminology, this notion helps heuristically separating two levels of judgment – called “formations” and “psychical functions” in Stumpf’s writings. Then I will give examples of how experimental subjects instantiated this logic. The musical and unmusical subjects, for instance, allowed grouping their reactions to stimuli into binary alternatives. Last, I will come back to the ways in which the apparatus spatially separated observers and subjects, so as to create different levels of previous knowledge. While the group’s insight into the experimental process has thereby become malleable, the control function is not restricted to juxtaposing one group with the other. Instead, both groups are subjected to control experiments that check on their default attitudes, as I will argue in conclusion.