AbstractArcades Project 1850. Image and Number in the Physiological Time Experiments of Hermann von Helmholtz. In January 1850, Hermann von Helmholtz (1821–1894) published a short report about his measurements concerning the propagation speed of “stimulations” in the living nerve. Historians of science such as Frederic Holmes and Kathryn Olesko have reconstructed the “investigative pathway” that led Helmholtz from his initial work on muscle action to the striking study of nervous time. Against the background of new archival findings, this paper argues that Helmholtz's investigative pathway also constituted a “semiotic pathway,” i. e. an arcade of signs that would capture and transmit his findings in appropriate ways. Drawing in particular on the curve recordings and the corresponding written explanations he sent to the Paris Academy of Science in September 1851, the paper shows that Helmholtz's graphical recordings were not meant as measurements. From the start, Helmholtz had carried out his time measurements by using an electromagnetic timing method suggested by the French physicist Claude Pouillet (1791–1868). In his 1850 report, Helmholtz had failed, however, to explain the physiological application of this method, even though his colleague and friend, Emil du Bois‐Reymond (1818–1896) had revised the report when translating it into French. In this situation, Helmholtz's curves served to illustrate the basic procedure of his previous experiments. In other words, they were indeed ‘images of precision’ (Holmes and Olesko) but not precise images.