Graziano & Raulin
Research Methods (9th edition)
Herman Helmholtz (1821-1894) was a German researcher in physics, physiology, and psychology. Along with Fechner and Weber, he helped to prepare the way for the emergence of scientific psychology in the late 19th Century.
Helmholtz's theoretical model was a highly mechanistic one--that is, he argued that sensory organs function like machines. He conducted research in vision and hearing and is credited with the invention of the ophthalmoscope, a device that is still used today for examining the retina. That invention made it possible to diagnose and treat disorders of the retina, and brought him worldwide attention. By the time he was 30, Helmholtz was famous and successful (Cahan, 1993).
He also studied the speed of the neural impulse, which had been thought to be instantaneous, or at least too fast to be measured. Helmholtz demonstrated that it was far from instantaneous.