time had become a critical issue in the field of astronomy, under the name of the "personal equation". Early researches by Friedrich Wilhelm Bessel (1784–1846) in Königsberg and Adolf Hirsch led to the development of a highly precise chronoscope by Matthäus Hipp that, in turn, was based on a design by Charles Wheatstone for a device that measured the speed of artillery shells (Edgell & Symes, 1906). Other timing instruments were borrowed from physiology (e.g., Carl Ludwig's kymograph) and adapted for use by the Utrecht ophthalmologist Franciscus Donders (1818–1899) and his student Johan Jacob de Jaager in measuring the duration of simple mental decisions. The 19th century was also the period in which physiology, including neurophysiology, professionalized and saw some of its most significant discoveries. Among its leaders were Charles Bell (1774–1843) and François Magendie (1783–1855) who independently discovered the distinction between sensory and motor nerves in the spinal column, Johannes Müller (1801–1855) who proposed the doctrine of specific nerve energies, Emil du Bois-Reymond (1818–1896) who studied the electrical basis of muscle contraction, Pierre Paul Broca (1824–1880) and Carl Wernicke (1848–1905) who identified areas of the brain responsible for different aspects of language, as well as Gustav Fritsch (1837–1927), Eduard Hitzig (1839–1907), and David Ferrier (1843–1924) who localized sensory and motor areas of the brain. One of the principal founders of experimental physiology, Hermann Helmholtz (1821–1894), conducted studies of a wide range of topics that would later be of interest to psychologists – the speed of neural transmission, the natures of sound and color, and of our perceptions of them, etc. In the 1860s, while he held a position in Heidelberg, Helmholtz engaged as an assistant a young physician named Wilhelm Wundt. Wundt employed the equipment of the physiology laboratory – chronoscope, kymograph, and various peripheral devices – to address more complicated psychological questions than had, until then, been investigated experimentally. In particular he was interested in the nature of apperception – the point at which a perception occupies the central focus of conscious awareness. In 1864 Wundt took up a professorship in Zürich, where he published his landmark textbook, Grundzüge der physiologischen Psychologie (Principles of Physiological Psychology, 1874). Moving to a more prestigious professorship in Leipzig in 1875, Wundt founded a laboratory specifically dedicated to original research in experimental psychology in 1879, the first laboratory of its kind in the world. In 1883, he launched a journal in which