Helmholtz pendulum, Berlin, Germany, 1895-1910. The swing of the pendulum stimulates a nerve in a muscle. To calculate the speed, the nerve is stimulated at different distances from the muscle. Nerve stimulation and muscle contraction are recorded on smoked glass paper. Hermann von Helmholtz (1821-1894), the German physicist and physician, used a similar pendulum myograph of his design to study the speed of nerve impulses in a frog. His researches found that the speed of nerve impulses was twenty metres per second. Earlier estimates were far slower.