“To appreciate the scientific value of Helmholtz’s little essay on the Conservation of Force, we should have to ask those to whom we owe the greatest discoveries in thermodynamics and other branches of modern physics, how many times they have read it over, and how often during their researches they felt the weighty statements of Helmholtz acting on their minds like an irresistible driving power.”

James Clerk Maxwell

“In his (Helmholtz’s) whole personality, his incorruptible judgment and in his modest manner he represented the dignity and truth of science. I was deeply touched by his human kindness. When in conversation he looked at me with his quite, searching but benevolent eyes, I was seized by a feeling of boundless, childlike devotion. I would have been prepared to confide in him anything which affected me deeply in the certainty of finding in him a just and mild counsellor, and an appreciative or even praising word from his mouth gave me greater happiness than all the success I could achieve in this world.”

Max Planck

Hermann Ludwig Ferdinand von Helmholtz made outstanding contributions to two areas of science—physiology and a physics. He made epoch-making contributions to the physiology of the eye and the ear. He invented (1851) the ophthalmoscope for inspecting the interior of the eye and ophthalmometer for measuring the eye’s curvature. He investigated colour vision and colour blindness. He also worked on hearing. He showed how the cochlea, the spiral-shaped part of the inner ear, resonates for different frequencies and analyses complex sounds into harmonic components. He is also well-known for his definitive statement of the first law of thermodynamics. He introduced the concept of free energy—the energy available to perform work.

Helmholtz’s investigations occupied almost the whole field of science—physiology, physiological optics, physiological acoustics, chemistry, mathematics, electricity and magnetism, meteorology and theoretical mechanics. R Steven Turner wrote: “Helmholtz devoted his life to seeking the great unifying principles underlying nature. His career began with one such principle, that of energy, and concluded with another, that of least action. No less than the idealistic generation before him, he longed to understand the ultimate, subjective sources of knowledge. That longing found expression in his determination to understand the role of the sense organs, as mediators of experience, in the synthesis of knowledge. To this continuity with the past Helmholtz and his generation brought two new elements, a profound distaste for metaphysical and an undeviating reliance on mathematics and mechanism. Helmholtz owed the scope and depth characteristic of his greatest work largely to the mathematical and experimental expertise which he brought to science…Helmholtz was the last great scholar whose work, in the tradition of Leibniz, embraced all the sciences, as well as philosophy and fine arts.”

Helmholtz was born in Potsdam, a city in Eastern Germany, on August 31, 1821 in a lower-middle class family that stressed education and culture. His father, August Ferdinand Julius Helmholtz served with distinction in Prussia’s fight against Napoleon. He studied at the newly established University of Berlin and worked as senior school master at the Potsdam Gymnasium. He taught German, classics, philosophy, mathematics and physics. It was a poorly paid job and Helmholtz was brought up in financially difficult circumstances. Helmholtz’s mother Caroline (nee Penne) was the daughter of a Hanoverian artillery officer, who had descended in the male line from William Penn, the founder of Pennsylvania, one of the 13 original States. Helmholtz was the eldest son of his parents. He had two sisters and a brother. He inherited from his mother ‘the placidity and reserve which marked his character in later life’.

Helmholtz was greatly influenced by his father, from whom came a rich, but mixed, intellectual heritage. From his father he learned the classical languages, as well as French, English, and Italian. It was his father who introduced him the philosophy of Immanuel Kant (1724-1804) and Johann Gottlieb Fichte (1762-1814) and to the approach to study the nature that flowed from their philosophical insights. This approach, which in the hands of early 19th century investigators, became a speculative science in which it was felt that for drawing scientific conclusions it was not necessary to gather empirical data from observations of the natural world because they could be deduced from philosophical ideas. Helmholtz’s later work was devoted to refuting this point of view. However, his empiricism was always deeply influenced by the aesthetic sensitivity passed on to him by his father. Music and painting played a greater part in his science.

Helmholtz began his school education at the age of seven. This is because of his delicate health. He entered the gymnasium in 1832. His performances as a student was generally good and he showed particular interest in exact science. After completing his education at the gymnasium he was keen to study physics. However, his father, who could not afford university fees, persuaded his son to take up the study of medicine. The State subsidized medical education but the same facility was not extended to those students, who opted for pure science. Thus in 1838 Helmholtz entered the Friedrich Wilhelm Medical Institute of Berlin, the Prussian military’s medical-training institute. Students at the Medical Institute were given some financial support in return for a commitment to serve five years as a military doctor after they qualified. They were also entitled to take classes at the University, a facility which was fully utilised by Helmholtz. He also studied a great deal on his own. Particularly he studied mathematics entirely on his own. He read works by Pierre Simon Laplace (1749-1827), Jean Baptiste Biot (1774-1862) and Daniel Bernoulli (1700-1782). At the Medical Institute he did research under the greatest German physiologist of the day, Johannes Peter Muller (1801-1858). He also learned to play the piano with a skill that later helped him in his work on the sensation of tone.

In 1842 he was qualified to be appointed as house-surgeon at a hospital, where he completed his doctoral thesis on the structure of the nervous system in invertebrates, the histological basis of nervous physiology and pathology. On graduation from the Medical Institute in 1843 he was appointed assistant surgeon to the Royal Hussars at Potsdam. His army duties were few and he had enough spare time to concentrate in his studies and research. He conducted experiments in a makeshift laboratory he set up in the barracks.

In 1847 Helmholtz published a very important paper titled “Uber dire Erhaltung der Kraft (On the Conservation of Force)”. In this paper Helmholtz argued in favour of conservation of energy. This paper, like all of his scientific works was characterised by a keen philosophical insight. He wrote: “….endeavours to ascertain the unknown causes of processes from their visible effects; it seeks to comprehend them according to the laws of causality. …Theoretical natural science must, therefore, if it is not to rest content with partial view of nature of things, take a position of harmony with the present conception of the nature of simple forces and the consequences of this conception. Its task will be completed when the reduction of phenomena to simple forces is completed, and when it can at the same time be produced that the reduction given is the only one possible which the phenomena will permit.” In this paper Helmholtz showed how the principle of conservation of kinetic energy could be derived from the assumption that work could not continually be produced from nothing. He then applied this principle of conservation of energy to a variety of situation and demonstrated that wherever energy appeared to be lost was in fact converted into heat energy. In fact this exactly happened in collisions, expanding gases, muscle contraction and in many other situations. The paper was very important contribution. It is true that others had conceived the idea of conservation of energy but then it was Helmholtz who first formulated the principle clearly and demonstrated it conclusively by scientific methods. This 1847 paper marked an epoch in both history of physiology and the history of physics. For physiology, it provided a fundamental statement about organic nature, which enabled physiologists henceforth to perform same kind of material and energy balance as done by their counterparts in physics and chemistry. This was the first blow that Helmholtz delivered to the concept of vitalism. The vitalists or the follower of the concept of vitalism believed that it would be impossible ever to reduce living processes to the ordinary mechanical laws of physics and chemistry.

Helmholtz’s 1847 paper marked an epoch in physical sciences because it provided the first clearest statement of the principle of conservation of energy; “Nature as a whole possesses a store of energy which cannot in any wise be added to or subtracted from.” This is known as the first law of thermodynamics. The first law of thermodynamics is sometimes summed up as: “You can’t get something for nothing” or “you cannot get more energy out of a reaction than you put into it” or “thermal energy input = useful energy + waste energy”. This was a corollary to Lavosier’s principle of the indestructibility of matter. Energy as matter cannot be created or destroyed. The first law of thermodynamics is one of the most revolutionary ideas in history of physics. A. C. Crombie, a science historian, wrote: “Its implications and the problems it posed dominated physics in the period between the electromagnetic researches of Faraday and Maxwell and the introduction of the quantum theory by Planck in 1900.”

The significance of Helmholtz’s contribution was widely acclaimed and it helped him to be free from his obligations to serve as a military doctor. The following year he was released from the military service to become lecturer at the Academy of Arts and assistant in the Anatomical Museum in Berlin. In 1849, he was appointed Associate Professor of Physiology and Director of the Physiological Institute at the Albertina University of Konigsberg. He married Olga von Velten on August 26, 1849 and settled down to an academic career. In 1849 he published the first part of his classic work on measurements of the time relations in the contraction of animal muscle and the rate of propagation in the nerve. The second part of this work was published two years later. This work of Helmholtz delivered another severe blow to the concept of vitalism. Helmholtz’s teacher Muller, who was a vitalist, used the nerve impulse as an example of a vital function and which meant it would never be submitted to experimental measurement. Helmholtz in his paper demonstrated that the impulse was perfectly measurable. He found that the movement was remarkably slow—it moved at a slow speed of some 27 metres per second. The measurement was possible because of the invention of the instrument called myograph by Helmholtz. This also illustrated Helmholtz’s ability to create new instruments. Helmholtz’s demonstration of the slowness of nerve impulse also supported those who believed that the movement of nerve impulse involved the rearrangement of molecules and not the mysterious passage of a vital force.

In 1851 Helmholtz invented the ophthalmoscope. This invention, which took him only two months to design and construct marked the beginning of Helmholtz’s studies on physiological optics. His studies dealt primarily with colour vision and dioptrics of the eye. The ophthalmoscope is still used as one of the most important instruments by physicians. It is used to examine retinal blood vessels, from which clues to high blood pressure and to arterial disease may be observed. He also invented the opthalmometer. The opthalmometer is used to measure the capacity of the eye to accommodate the changing optical circumstances and this way it enables among other things, the proper prescription of eyeglasses. With the combined knowledge of ophthalmology and physiological optics, Helmholtz was able to demonstrate the relationship between the direction of the incident and emergent light.

Helmholtz’s researches on the eye were incorporated in his Handbook of Physiological Optics. The first volume of his famed Handbook appeared in 1856 and a second volume in 1867. It was in German and its English translation appeared 60 years later. The great work was acclaimed worldwide. In this Helmholtz introduced the three variables to characterise a colour—hue, saturation and brightness. These are still used. It was Helmholtz, who first unequivocally demonstrated that the colours which Newton had seen in his spectrum are different from colours applied to a white base using pigments. The spectral colours possess greater saturation and they shine more intensely. While the spectral colours are mixed additively but pigments are mixed subtractively. In each case a different set of rules govern their combination.

Helmholtz was one of the first German scientists to appreciate the work in electrodynamics by Michael Faraday and James Clerk Maxwell. Summarising the contributions of Helmholtz and his illustrious student Hertz, David Cahan wrote: “Helmholtz’s most gifted student was Heinrich Hertz…In the 1860s and 1870s, Helmholtz was much concerned with evaluating competing theories of electrodynamics. Hertz became Helmholtz’s disciple in his visionary program to establish firm foundations for electrodynamics…Hertz’s death in Bonn on 1 January 1894 and Helmholtz’s in Berlin on 8 September 1894, marked the end of classical physics and its mechanical worldview. Helmholtz sought to unify physics, if not all the sciences, and indeed hoped for the ultimate unification of all culture. Hertz, by contrast, worked within the physics that Helmholtz had outlined. Together they cleared the ground in electrodynamics and mechanics and so paved the way for Max Planck, Albert Einstein, and others at the turn of the century. Furthermore, Hertz’s results in electrodynamics proved as seminal for technology as for physical theory, for they set the stage for revolution in wireless communication.”

References

1. James, Ioan, Remarkable Physicists: From Galileo to Yukawa, Cambridge: Cambridge University Press, 2004.
   
   
2. Spangenburg, Ray and Diane K. Moser, The History of Science In the Nineteenth Century, Hyderabad: Universities Press (India) Ltd., 1994.
   
   
3. Cahan, David, “Helmholtz, Hermann von (1821-1894)” in The Companion to The History of Modern Science, Oxford: Oxford University Press, 2003.
   
   
4. The Cambridge Dictionary of Scientists (Second Edition), Cambridge: Cambridge University Press, 2002.
   
   
5. Chambers Biographical Dictionary (Centenary Edition), Edinburgh & New York: Chambers Harrap Publishers Ltd., 1997.
   
   
6. A Dictionary of Scientists. Oxford: Oxford University Press, 1999.