Helmholtz’ physical physiology

The second half of the 19th century is undoubtedly one of the most productive and interesting epochs in the history of Western science (Hanslick’s writing on «On Musical Beauty» also dates from this period). In the field of music aesthetics, the half-century meant above all the opening of a door: access to the scientific theory of music in general and the physiologically oriented theory of music in particular.

A polymath whose prolific output is comparable to that of Johann Sebastian Bach towers above all others: the physicist, physician, mathematician and physiologist Hermann von Helmholtz (1821 – 1894). His contributions to scientific progress range from the mathematical justification of the law of conservation of energy and work on color theory, including the invention of the ophthalmoscope, to physiological acoustics. The latter is set out in his classic work «Die Lehre von den Tonempfindungen als physiologische Grundlage für die Theorie der Musik». It dates from the time of his work in Heidelberg, where he represented modern, physically oriented science alongside the chemist Gustav Bunsen (still known to some as the namesake of the Bunsen burner) and the physicist Gustav Kirchhoff, incidentally with an annual salary of 3600 guilders, which was unusually high for the time.

The scientific orientation in Heidelberg also had political motives: After the 1848 revolution, the state endeavored to improve material living conditions in order to avoid further uprisings. The scientists were to contribute to this by optimizing agriculture. Helmholtz wrote to his friend Emil Heinrich du Bois-Reymond in 1858: «I fear that the legal provision that makes the physiological practical course a compulsory college for the people of Baden is an exaggeration of Enlightenment principles and could become very troublesome for me.» However, Helmholtz’s time in Heidelberg was not just a period of scientific activity. It was also a time of numerous military conflicts, some of which he took part in: In the Franco-Prussian War of 1870/71, he served as a field doctor in the Battle of Wörth.

Helmholtz’s work in physical optics had already led him to realize that not all physiological phenomena could be explained by physical means alone, but that psychology played an important role. In a ceremonial address in 1862, he almost reluctantly admitted that «the physiology of the sensory organs is closely connected with psychology in that it demonstrates the results of psychological processes in sensory perceptions.» Helmholtz did not deal with acoustic problems until after completing a handbook on physiological optics, which had already sensitized him to the complex interplay between physics, physiology and psychology.

The basis for his acoustic investigations is the earlier insight that the nerve conduction velocity is a finite (and temperature-dependent) quantity. This also enabled Helmholtz to show that du Bois-Reymond’s assumption that the electrical nerve impulse has a molecular continuation must be correct. These arguments represent an important victory of the physical view of psychology over metaphysical constructions, such as the vitalism of the time. Finally, Helmholtz was able to show that musical sound is based on overtones and that the ear can perceive complex overtone mixtures. Helmholtz thus also overturned a principle that had previously been established by the physicist Georg Simon Ohm (1789 – 1854). It states that the human ear can only perceive simple harmonic vibrations.

Helmholtz’s interest in physiology seems to have been exhausted with the «Doctrine of the Sensations of Sound». He later moved from Heidelberg to Berlin, where he only dealt with questions of mathematics and physics.

In the preface to the «Doctrine», Helmholtz outlines the future structure of the study of hearing:

The investigation of the processes in each of our sense organs generally has three distinct parts. The first part is to investigate how the agent that excites the sensation, i.e. light in the eye and sound in the ear, is conducted to the sensory nerves. We can call this first part the physical part of the corresponding physiological investigation. Secondly, we must examine the various excitations of the nerves themselves, which correspond to various sensations, and finally the laws by which such sensations give rise to ideas of certain external objects, i.e. perceptions. Thus there is, secondly, a preferably physiological part of the investigation, which deals with the sensations, and thirdly, a psychological part, which deals with the perceptions.

Incidentally, one of his assistants during his time in Heidelberg was Wilhelm Wundt. In 1879, Wundt founded the first institute for experimental psychology in the history of science in Leipzig and thus became the father of practically all subsequent music psychologists.