In 2019 a collection of letters from the nineteenth-century natural philosopher Robert Were Fox was discovered in his home at Penjerrick in Cornwall. Fox came to the attention of scientific audiences for experimentally establishing that temperature increases with depth beneath the Earth's surface, and later secured fame for his magnetic dipping needle, developed to measure terrestrial magnetic phenomena. The newly uncovered Penjerrick letters constitute a valuable archival discovery with important historical ramifications for our understanding of Fox's work and its place within nineteenth-century science. As well as highlighting the central role of networking in promoting provincial science, the letters reveal the prominence of the Cornish mine as a site of experiment within British scientific culture. These venues presented Fox with unique spaces in which to scrutinize nature, but such philosophical investigations were unverifiable within a laboratory and appeared susceptible to inaccuracies arising from the working conditions of this uncontrollable environment. Nevertheless, the Cornish mine was crucial to the development of Fox's dipping needle, which became the premier device for making magnetic observations at sea in the 1840s. In this article, I demonstrate the epistemologically problematic nature of the mine as an experimental space that was to take on a central role in the worldwide magnetic survey that historians have described as the ‘Magnetic Crusade’.
SPICE-Aided Compact Electrothermal Model of Impulse Transformers