Hermann Helmholtz (1821-1894)

Helmholtz was the son of the headmaster of the Potsdam Gymnasium, a newly established type of school for Prussian boys that emphasized a classical curriculum. There, Helmholtz absorbed Kant’s philosophy along with Fichte’s “nature philosophy,” a highly subjective view of science that emphasized the primacy of philosophical thinking over the collection and analysis of empirical data. Later in his career many of Helmholtz’s scientific contributions would help overturn nature philosophy. After graduating from the gymnasium Helmholtz wanted to study physics but because of his family’s inability to financially support him entered medical school instead. Medical education in Prussia was free to men who pledged to spend five years as army doctors following completion of their studies. At the Friedrich Wilhelm Medical Institute in Berlin he studied under Johannes Müller.

However, Helmholtz and his fellow students soon secretly rebelled against Müller’s vitalist views. Some of them founded the Berlin Physical Society in response; Helmholtz soon joined that group. That society was dedicated toward providing strictly physical explanations for biological phenomena. Helmholtz and three others prepared a document stating their mechanistic views with each of them signing it using a drop of their own blood (Coren, 2003). After graduating from medical school Helmholtz was assigned to an army post back in Potsdam. His duties were minimal and he was able to conduct his own research there and, while on leave, in Berlin. His research gained him some attention and an early release from his army commitment.

In 1847, very early in his academic career, he published one of his most important findings, a pamphlet on the conservation of energy. In it, he clearly explained and mathematically demonstrated that heat and energy were equivalent and that neither was ever destroyed. That relationship is now called the First Law of Thermodynamics. Helmholtz’s elucidation of that law did much to finally bury vitalist approaches to biology. The reception by other scientists to that law was mixed at first. Younger scientists, in general, approved whereas older scientists, did not. Thus, the discovery of conservation of energy did not, at first, make Helmholtz famous.

Two of his subsequent discoveries did so, however. The first of those was his measurement of the speed of the nerve impulse and the second was his development of the ophthalmoscope, an instrument that permitted him and others to see into the living human eye clearly for the first time. Soon after, he published the Handbook of Physiological Optics. In that book he combined his deep knowledge of physics with his interest in physiology. His goal was to trace completely the route taken by nerve signals as they pass from the eye to the brain. Helmholtz was unaware of the complexity of the task he had set for himself. That question remains yet unanswered today. Another of his important contributions to the physiology of vision was his theory of color perception. He amplified the earlier ideas of Thomas Young (1773-1829) to create the familiar Young-Helmholtz trichromatic theory of color vision. That theory holds that humans perceive color because of the simultaneous activity of three different types of visual receptors, the cones of the eye. The Young-Helmholtz theory maintains that the activity of millions of cones; tuned to red, green, or blue; make color vision possible. Helmholtz also studied the physics of sound and the physiology of the ear. His interest in physical phenomena preceded his research in the physiology of hearing. Once again, he developed instruments to aid him in his physiological research. In the case of hearing, he developed the “Helmholtz resonator,” (see Figure 7.4) a device that could isolate the prime tone of a sound. The small end of the resonator was coated with wax (to provide a good seal) and inserted into the ear.

---------------Insert Figure 7.4 about here [Helmholtz resonators]---------------

The larger end was also open. Each resonator was tuned to a specific tone. When a complex sound was presented the wearer could identify the particular prime tone because it could be heard clearly. All other sounds were muffled. Later, he built more advanced, adjustable, electric resonators that could be tuned to any specific pure tone. Helmholtz pioneered the study of psychoacoustics. His student, Heinrich Hertz (1857-1894), extended Helmholtz’s early steps beyond sound and into the study of radio waves and other oscillating phenomena. Helmholtz also published many articles on physical and mathematical topics including vortex motion, hydrodynamics, and non-Euclidean geometry, or geometries that allow parallel lines in space to touch.

When Helmholtz realized that those non-Euclidean geometries existed and that they were just as logically consistent as Euclidean geometry he finally broke with Kant’s nativist conception of space. (Recall that Kant believed that humans did not need to learn about space, time, or causality. That knowledge, he maintained, was already present at birth.) Helmholtz came to believe that humans learned about the nature of space through experience. The fact that other geometries existed was the clincher for him. How could Kant be correct if more than one type of space existed? Helmholtz finished his years as the Director of the Institute of Physics at the University of Berlin where he laid the earliest foundations of 20th century modern physics.

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