Wednesday

What can alchemical imagery tell us about alchemy as actually practiced? For medieval practitioners, observable markers were essential for evaluating the progress of their work. Visual signs, including color changes and transformations, might serve as an evidentiary strategy—practitioners could increase confidence in their own work by physically reconstructing the authoritative chemical effects, often described as signs, or “tokens,” attested in the books of alchemical philosophers. For both practitioners and their readers, however, the problem was knowing how to distinguish between representations that alluded to conceptual or theoretical material, and those that portrayed actual, observable effects—the signa beloved of past authorities. This distinction is complicated by the fact that the meaning of images tends to change as they are copied over time, gradually becoming separated from their original context. 

In this paper, I combine my own research on alchemical imagery with my interest in the modern-day reconstruction of historical recipes and experiments, to reconstruct an influential set of processes described by the English canon George Ripley in his Medulla alchimiae (1476). Ripley and his readers, I argue, blended their own experimental observations with imagery drawn from diverse literary and artistic traditions, to generate authority for both individual practices and alchemy as a whole. By linking these figurative images to practical content, I seek to recover an “alchemist’s eye” view of the material world: a view that grasps the details of alchemy as actually practiced, while comprehending how changing contexts also brought about the transmutation of alchemical imagery—and its meanings— over time. 

In 1850, A. W. Hofmann claimed a major advance in understanding nitrogen-containing organic compounds.  Hofmann’s ammonia type was rapidly accepted, beginning to resolve longstanding disciplinary disputes and playing a key role in type theory’s rise to dominance.  What made Hofmann’s work so persuasive and why did it provide such a stable basis for theory-building?  Answering these questions takes us to the heart of Hofmann’s approach to experiment and theory, and to what I have called “laboratory reasoning.”  As we shall see, deciding what experiments to perform, and which results were valid and why, was crucial to Hofmann’s expertise.  Learning how he responded when things went wrong clarifies why other chemists trusted his results – even though they had no intention of seeking to replicate them – and why they continued using the ammonia type long after type theory was forgotten.

The stated criteria for what constituted rigorous or “exact” anatomical investigation changed over the course of the sixteenth and seventeenth centuries. It is clear that a renewed interest in Galenic and Aristotelian methods for dissecting, organizing research, and constructing arguments in anatomy played a major role, as did the rise of various genres of medical and anatomical history. Ocular anatomy around the turn of the seventeenth century, however, was unique in that the fields of anatomy, natural philosophy, and mathematics (i.e., the “middle science” of optics) became deeply intertwined on questions related to vision. For a brief period many investigators began hunting for the correct sizes, shapes, relative positions, and refractive powers of the parts of a living eye via dissection and experimentation, and only subsequently to construct the physics and mathematics of their visual theory upon this foundation. This process, however, was fraught with difficulties.

Kepler’s Dioptrice arguably inaugurated a transformation of optics from the science of sight, whose main purpose was to understand first-person visual experience, to an optics more familiar to us today: a science of light whose primary aim is to understand how light interacts with matter, and especially to understand projected images. Nevertheless, up through the first half of the seventeenth century mathematical optics was still largely a science of sight. Many investigators attempted to bring visual experience under greater control by inventing new, contrived visual experiences and experiments, and by integrating them with anatomical and mathematical findings.

Christoph Scheiner’s 1619 The Eye, That Is, the Foundation of Optics perhaps best exemplifies this attempt to perform careful, quantitative ocular anatomy and to marry it with contrived first-person visual experiences and experiments, all with the goal of articulating a theory of vision.

In 1912 a debate started between Karl von Hess and Karl von Frisch about color vision in fish. Hess denied color vision, Frisch took the opposite view. The discussion continues until the 1920s and expands – this part of the argument is better known – to color vision in bees. Several reasons can be given for the duration of the debate: first, competing disciplinary claims – Hess is a physiologist specialized in ophthalmology, Frisch a trained zoologist, second, a strong hierarchical imbalance – Hess is a full professor, Frisch at the beginning just a ‘Privatdozent’ (and on top of that both are active at the Munich University), and third, both Hess and Frisch tend to polemic. In my contribution, however, I would like to deal exclusively with the experimental strategies of Hess and Frisch. In particular I am interested in their explicit and implicit concepts of how to properly study color vision in fish.