The instruments of expeditionary science and the reworking of nineteenth-century magnetic experiment

During the mid-nineteenth century, British naval expeditions navigated the world as part of the most extensive scientific undertaking of the age. Between 1839 and the early 1850s, the British government orchestrated a global surveying of the Earth's magnetic phenomena: this was a philosophical enterprise of unprecedented state support and geographical extent. But to conduct this investigation relied on the use of immensely delicate instruments, known as ‘dipping needles’. The most celebrated of these were those of Robert Were Fox, designed and built in Cornwall. Yet these devices were difficult to physically maintain and ensuring accuracy throughout a magnetic experiment was challenging. In 2020, Crosbie Smith and I took an original Fox dipping needle on a voyage from Falmouth to Cape Town, retracing the routes of survey expeditions, including James Clark Ross's 1839–43 Antarctic venture. The article offers an account of our experiences, combined with historical reports of the instrument's past performances. It explores the instrumental challenges involved in nineteenth-century global experimental investigation. The great problem for the British magnetic survey was of coordinating standardized experimental measurements over vast expanses of space and time. As this article argues, this was very much a question of instrumental management, both of dipping needles and of human performers.