Towards the end of the 1840s, Hermann von Helmholtz began to investigate experimentally the propagation of stimuli within nerves. Helmholtz's experiments on animals and human subjects opened a research field that in the following decades was intensively explored by neurophysiologists and experimental psychologists. Helmholtz's pioneering investigations justify the central place he occupies in accounts of the history of modern psychophysiology. Studying the concrete experimental settings and their local contexts shows how deeply the work of scholars such as Helmholtz is embedded in the history of culture and technology. In particular, the rapidly growing technologies of electromagnetism, which gave rise to telegraphy and electric clocks, facilitated the time measurements of 19th-century physiologists and psychologists.