A Dim Portrait

This has been a portrait of Helmholtz the scientist and famous intellect. What
was he like as a human being? In spite of his extraordinary prominence, that
question is difficult to answer. The authorized biography, by Leo Ko¨nigsberger,
is faithful to the facts of Helmholtz’s life and work, but too admiring to be reliably
whole in its account of his personal traits. Helmholtz’s writings are not
much help either, even though many of his essays were intended for lay audiences.
His style is too severely objective to give more than an occasional
glimpse of the feeling and inspiration he brought to his work. We are left with
fragments of the human Helmholtz, and, like archaeologists, we must try to
piece them together.
We know that Helmholtz had a marvelous scientific talent, and an immense
capacity for hard work. Sessions of intense mental effort were likely to leave
him exhausted and sometimes disabled with a migraine attack, but he always
recovered, and throughout his life had the working habits of a workaholic.
He was blessed with two happy marriages. The death of his first wife, Olga,
after she spent many years as a semiinvalid, left him incapacitated for months
with headaches, fever, and fainting fits. As always, though, workwas his tonic,
and in less than two years he had married again. His second wife, Anna, was
young and charming, “one of the beauties of Heidelberg,” Helmholtz wrote to
Thomson. She was a wife, wrote Ko¨nigsberger, “who responded to all [of Helmholtz’s]
needs . . . a person of great force of character, talented, with wide views
and high aspirations, clever in society, and brought up in a circle in which intelligence
and character were equally well developed.” Anna’s handling of the
household and her husband’s rapidly expanding social commitments contributed
substantially to the Helmholtz success story in Heidelberg and Berlin.
To achieve what he did, Helmholtz must have been intensely ambitious. Yet
he seems to have traveled the road to success without pretension and with no
question about his integrity, scientific or otherwise. Max Planck, a man whose
opinion can be trusted on the subjects of integrity and intellectual leadership
without pretension, wrote about his friendship with Helmholtz in the 1890s in
Berlin:
I learned to know Helmholtz . . . as a human being, and to respect him as a
scientist. For with his entire personality, integrity of convictions and modesty
of character, he was the very incarnation of the dignity and probity of science.
These traits of character were supplemented by a true human kindness, which
touched my heart deeply. When during a conversation he would lookat me
with those calm, searching, penetrating, and yet so benign eyes, I would be overwhelmed by a feeling of boundless filial trust and devotion, and I would
feel that I could confide in him, without reservation, everything I had on my
mind.
Others, who saw Helmholtz from more of a distance, had different impressions.
Englebert Broda comments that Boltzmann “had the greatest respect for
Helmholtz the universal scientist, [but] Helmholtz the man . . . left him cold.”
Among his students and lesser colleagues, Helmholtz was called the “Reich
Chancellor of German Physics.”
There can hardly be any doubt that Helmholtz had a passionate interest in
scientific investigation and an encyclopedic grasp of the facts and principles of
science. Yet something contrary in his character made it difficult for him to communicate
his feelings and knowledge to a class of students.We are again indebted
to Planck’s frankness for this picture of Helmholtz in the lecture hall (in Berlin):
“It was obvious that Helmholtz never prepared his lectures properly. He spoke
haltingly, and would interrupt his discourse to lookfor the necessary data in his
small notebook; moreover, he repeatedly made mistakes in his calculations at the
blackboard, and we had the unmistakable impression that the class bored him at
least as much as it did us. Eventually, his classes became more and more deserted,
and finally they were attended by only three students; I was one of the
three.”
Helmholtz viewed scientific study in a special, personal way. The conventional
generalities required by students in a course of lectures may not have been
for him the substance of science. At any rate, Helmholtz was not the first famous
scientist to fail to articulate in the classroom the fascination of science, and (as
those who have served university scientific apprenticeships can attest) not the
last.
The intellectual driving force of Helmholtz’s life was his never-ending search
for fundamental unifying principles. He was one of the first to appreciate that
most impressive of all the unifying principles of physics, the conservation of
energy. In 1882, he initiated one of the first studies in the interdisciplinary field
that was soon to be called physical chemistry. His workon perception revealed
the unity of physics and physiology. Beyond that, his theories of vision and
hearing probed the aesthetic meaning of color and music, and built a bridge
between art and science. He expressed, as few had before or have since, a unity
of the subjective and the objective, of the aesthetic and the intellectual.
He had hoped to find a great principle from which all of physics could be
derived, a unity of unities. He devoted many years to this effort; he thought that
the “least-action principle,” discovered by the Irish mathematician and physicist
William Rowan Hamilton, would serve his grand purpose, but Helmholtz died
before the workcould be completed. At about the same time, Thomson was failing
in an attempt to make his dynamical theory all-encompassing. In the twentieth
century, Albert Einstein was unsuccessful in a lengthy attempt to formulate a unified
theory of electromagnetism and gravity. In the 1960s, the particle physicists
Sheldon Glashow, Abdus Salam, and StevenWeinberg developed a unified theory
of electromagnetism and the nuclear weakforce. The search goes on for stillbroader
theories, uniting atomic, nuclear, and particle physics with the physics
of gravity. We can hope that these quests for a “theory of everything” will eventually
succeed. But we may have to recognize that there are limits. Scientists may
never see the day when the unifiers are satisfied and the diversifiers are not busy.

Physics

By 1871, the year he reached the age of fifty, Helmholtz had accomplished more
than any other physiologist in the world, and he had become one of the most
famous scientists in Germany. He had worked extremely hard, often to the detriment
of his mental and physical health. He might have decided to relax his
furious pace and become an academic ornament, as others with his accomplishments
and honors would have done. Instead, he embarked on a new career, and
an intellectual migration that was, and is, unique in the annals of science. In
1871, he went to Berlin as professor of physics at the University of Berlin.
The conversion of the physiologist to the physicist was not a miraculous rebirth,
however. Physics had been Helmholtz’s first scientific love, but circumstances
had dictated a career in medicine and physiology. Always a pragmatist,
he had explored the frontier between physics and physiology, earned a fine reputation,
and more than anyone else, established the new science of biophysics.
But his fascination with mathematical physics, and his ambition, had not faded.
With the death of Gustav Magnus, the Berlin professorship was open. Helmholtz
and Gustav Kirchhoff, professor of physics at Heidelberg, were the only candidates;
Kirchhoff preferred to remain in Heidelberg. “And thus,” wrote du Bois-
Reymond, “occurred the unparalleled event that a doctor and professor of physiology
was appointed to the most important physical post in Germany, and
Helmholtz, who called himself a born physicist, at length obtained a position
suited to his specific talents and inclinations, since he had, as he wrote to me,
become indifferent to physiology, and was really only interested in mathematical
physics.”
So in Berlin Helmholtz was a physicist. He focused his attention largely on
the topic of electrodynamics, a field he felt had become a “pathless wilderness”
of contending theories. He attacked the work of Wilhelm Weber, whose influence
then dominated the theory of electrodynamics in Germany. Before most of his
colleagues on the Continent, Helmholtz appreciated the studies of Faraday and
Maxwell in Britain on electromagnetic theory. Heinrich Hertz, a student of Helmholtz’s
and later his assistant, performed experiments that proved the existenceof electromagnetc waves and confirmed Maxwell’s theory. Also included among
Helmholtz’s remarkable group of students and assistants were Ludwig Boltzmann,
Wilhelm Wien, and Albert Michelson. Boltzmann was later to lay the
foundations for the statistical interpretation of thermodynamics (see chapter 13).
Wien’s later workon heat radiation gave Max Planck, professor of theoretical
physics at Berlin and a Helmholtz prote´ge´, one of the clues he needed to write
a revolutionary paper on quantum theory. Michelson’s later experiments on the
velocity of light provided a basis for Einstein’s theory of relativity. Helmholtz,
the “last great classical physicist,” had gathered in Berlin some of the theorists
and experimentalists who would discover a new physics.

Physiology

After 1847, Helmholtz was only intermittently concerned with matters relating
to thermodynamics. His worknow centered on medical science, specifically the
physical foundations of physiology. He wanted to build an edifice of biophysics
on the groundworklaid by Mu¨ ller, his Berlin professor, and by his colleagues du
Bois-Reymond, Ludwig, and Bru¨ cke, of the 1847 school. Helmholtz’s rise in the
scientific and academic worlds was spectacular. For six years, he was professorof physiology at Ko¨nigsberg, and then for three years professor of physiology and
anatomy at Bonn. From Bonn he went to Heidelberg, one of the leading scientific
centers in Europe. During his thirteen years as professor of physiology at Heidelberg,
he did his most finished workin biophysics. His principal concerns were
theories of vision and hearing, and the general problem of perception. Between
1856 and 1867, he published a comprehensive workon vision, the three-volume
Treatise on Physiological Optics, and in 1863, his famous Sensations of Tone, an
equally vast memoir on hearing and music.
Helmholtz’s workon perception was greatly admired during his lifetime, but
more remarkable, for the efforts of a scientist working in a research field hardly
out of its infancy, is the respect for Helmholtz still found among those who try
to understand perception. Edward Boring, author of a modern text on sensation
and perception, dedicated his bookto Helmholtz and then explained: “If it be
objected that books should not be dedicated to the dead, the answer is that Helmholtz
is not dead. The organism can predecease its intellect, and conversely. My
dedication asserts Helmholtz’s immortality—the kind of immortality that remains
the unachievable aspiration of so many of us.”

Pros and Cons

Helmholtz’s youthful effort in his paper (he was twenty-six in 1847), read to the
youthful members of the Berlin Physical Society, was received with enthusiasm.
Elsewhere in the scientific world the reception was less favorable. Helmholtz
submitted the paper for publication to Poggendorff’s Annalen, and, like Mayer
five years earlier, received a rejection. Once again an author with importantthings to say about the energy concept had to resort to private publication. With
du Bois-Reymond vouching for the paper’s significance, the publisher G. A. Reimer
agreed to bring it out later in 1847.
Helmholtz commented several times in later years on the peculiar way his
memoir was received by the authorities. “When I began the memoir,” he wrote
in 1881, “I thought of it only as a piece of critical work, certainly not as an
original discovery. . . . I was afterwards somewhat surprised over the opposition
which I met with among the experts . . . among the members of the Berlin academy
only C. G. J. Jacobi, the mathematician, accepted it. Fame and material reward
were not to be gained at that time with the new principle; quite the opposite.”
What surprised him most, he wrote in 1891 in an autobiographical
sketch, was the reaction of the physicists. He had expected indifference (“We all
know that. What is the young doctor thinking about who considers himself called
upon to explain it all so fully?”). What he got was a sharp attackon his conclusions:
“They [the physicists] were inclined to deny the correctness of the law . . .
to treat my essay as a fantastic piece of speculation.”
Later, after the critical fog had lifted, priority questions intruded. Mayer’s papers
were recalled, and obvious similarities between Helmholtz and Mayer were
pointed out. Possibly because resources in Potsdam were limited, Helmholtz had
not read Mayer’s papers in 1847. Later, on a number of occasions, he made it
clear that he recognized Mayer’s, and also Joule’s, priority.
The modern assessment of Helmholtz’s 1847 paper seems to be that it was, in
some ways, limited. It certainly did cover familiar ground (as Helmholtz had
intended), but it did not succeed in building mathematical and physical foundations
for the energy conservation principle. Nevertheless, there is no doubt
that the paper had an extraordinary influence. James ClerkMaxwell, prominent
among British physicists in the 1860s and 1870s, viewed Helmholtz’s general
program as a conscience for future developments in physical science. In an appreciation
of Helmholtz, written in 1877, Maxwell wrote: “To appreciate the full
scientific value of Helmholtz’s little essay . . . we should have to askthose 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.”
What Maxwell and other physicists were paying attention to was passages
such as this: “The task[of theoretical science] will be completed when the reduction
of phenomena to simple forces has been completed and when, at the
same time, it can be proved that the reduction is the only one which the phenomena
will allow. This will then be established as the conceptual form necessary
for understanding nature, and we shall be able to ascribe objective truth to
it.” To a large extent, this is still the program of theoretical physics.

Die Erhaltung der Kraft

If medicine was not Helmholtz’s first choice, it nevertheless served him (and he
served medicine) well, even when circumstances were trying. His medical scholarship
stipulated eight years of service as an army surgeon. He tookup this
service without much enthusiasm. Life as surgeon to the regiment at Potsdam
offered little of the intellectual excitement he had found in Berlin. But to an
extraordinary degree, Helmholtz had the ability to supply his own intellectual
stimulation. Although severely limited in resources, and unable to sleep after
five o’clockin the morning when the bugler sounded reveille at his door, he
quickly started a full research program concerned with such topics as the role of
metabolism in muscle activity, the conduction of heat in muscle, and the rate of
transmission of the nervous impulse.
During this time, while he was mostly in scientific isolation, Helmholtz wrote
the paper on energy conservation that brings him to our attention as one of the
major thermodynamicists. (Once again, as in the stories of Carnot, Mayer, and
Joule, history was being made by a scientific outsider.) Helmholtz’s paper had
the title U¨ ber die Erhaltung der Kraft (On the Conservation of Force), and it was
presented to the Berlin Physical Society, recently organized by du Bois-Reymond,
and other students of Mu¨ ller’s, and Gustav Magnus, in July 1847.
As the title indicates, Helmholtz’s 1847 paper was concerned with the concept
of “force”—in German, “Kraft”—which he defined as “the capacity [of matter] to
produce effects.” He was concerned, as Mayer before him had been, with a composite
of the modern energy concept (not clearly defined in the thermodynamic
context until the 1850s) and the Newtonian force concept. Some of Helmholtz’s
uses of the word “Kraft” can be translated as “energy” with no confusion. Others
cannot be interpreted this way, especially when directional properties are assumed,
and in those instances “Kraft” means “force,” with the Newtonian
connotation.
Helmholtz later wrote that the original inspiration for his 1847 paper was his
reaction as a student to the concept of “vital force,” current at the time among
physiologists, including Mu¨ ller. The central idea, which Helmholtz found he
could not accept, was that life processes were controlled not only by physical
and chemical events, but also by an “indwelling life source, or vital force, which
controls the activities of [chemical and physical] forces. After death the free action
of [the] chemical and physical forces produces decomposition, but during
life their action is continually being regulated by the life soul.” To Helmholtz
this was metaphysics. It seemed to him that the vital force was a kind of biological perpetual motion. He knew that physical and chemical processes did not
permit perpetual motion, and he felt that the same prohibition must be extended
to all life processes.
Helmholtz also discussed in his paper what he had learned about mechanics
from seventeenth- and eighteenth-century authors, particularly Daniel Bernoulli
and Jean d’Alembert. It is evident from this part of the paper that a priori beliefs
are involved, but the most fundamental of these assumptions are not explicitly
stated. The science historian Yehuda Elkana fills in for us what was omitted:
“Helmholtz was very much committed—a priori—to two fundamental beliefs: (a)
that all phenomena in physics are reducible to mechanical processes (no one
who reads Helmholtz can doubt this), and (b) that there be some basic entity in
Nature which is being conserved ([although] this does not appear in so many
words in Helmholtz’s work).” To bring physiology into his view, a third belief
was needed, that “all organic processes are reducible to physics.” These general
ideas were remarkably like those Mayer had put forward, but in 1847 Helmholtz
had not read Mayer’s papers.
Helmholtz’s central problem, as he saw it, was to identify the conserved entity.
Like Mayer, but independently of him, Helmholtz selected the quantity “Kraft”
for the central role in his conservation principle. Mayer had not been able to
avoid the confused dual meaning of “Kraft” adopted by most of his contemporaries.
Helmholtz, on the other hand, was one of the first to recognize the ambiguity.
With his knowledge of mechanics, he could see that when “Kraft” was
cast in the role of a conserved quantity, the term could no longer be used in the
sense of Newtonian force. The theory of mechanics made it clear that Newtonian
forces were not in any general way conserved quantities.
This reasoning brought Helmholtz closer to a workable identification of the
elusive conserved quantity, but he (and two other eminent thermodynamicists,
Clausius and Thomson) still had some difficult conceptual ground to cover. He
could follow the lead of mechanics, note that mechanical energy had the conservation
property, and assume that the conserved quantity he needed for his
principle had some of the attributes (at least the units) of mechanical energy.
Helmholtz seems to have reasoned this way, but there is no evidence that he got
any closer than this to a full understanding of the energy concept. In any case,
his message, as far as it went, was important and eventually accepted. “After [the
1847 paper],” writes Elkana, “the concept of energy underwent the fixing stage;
the German ‘Kraft’ came to mean simply ‘energy’ (in the conservation context)
and later gave place slowly to the expression ‘Energie.’ The Newtonian ‘Kraft’
with its dimensions of mass times acceleration became simply our ‘force.’ ”
I have focused on the central issue taken up by Helmholtz in his 1847 paper.
The paper was actually a long one, with many illustrations of the conservation
principle in the physics of heat, mechanics, electricity, magnetism, and (briefly,
in a single paragraph) physiology.

Medicine and Physics

Helmholtz, like Mayer, was educated for a medical career. He would have preferred
to study physics and mathematics, but the only hope for scientific training,
given his father’s meager salary as a gymnasium teacher, was a government scholarship in medicine. With the scholarship, Helmholtz studied at the Friedrich-
Wilhelm Institute in Berlin and wrote his doctoral dissertation under Johannes
Mu¨ ller. At that time, Mu¨ ller and his circle of gifted students were laying the
groundworkfor a physical and chemical approach to the study of physiology,
which was the beginning of the disciplines known today as biophysics and biochemistry.
Mu¨ ller’s goal was to rid medical science of all the metaphysical excesses
it had accumulated, and retain only those principles with sound empirical
foundations. Helmholtz joined forces with three of Mu¨ ller’s students, Emil du
Bois-Reymond, Ernst Bru¨ cke, and Carl Ludwig; the four, known later as the “1847
group,” pledged their talents and careers to the taskof reshaping physiology into
a physicochemical science.

Medicine and Physics

Helmholtz, like Mayer, was educated for a medical career. He would have preferred
to study physics and mathematics, but the only hope for scientific training,
given his father’s meager salary as a gymnasium teacher, was a government scholarship in medicine. With the scholarship, Helmholtz studied at the Friedrich-
Wilhelm Institute in Berlin and wrote his doctoral dissertation under Johannes
Mu¨ ller. At that time, Mu¨ ller and his circle of gifted students were laying the
groundworkfor a physical and chemical approach to the study of physiology,
which was the beginning of the disciplines known today as biophysics and biochemistry.
Mu¨ ller’s goal was to rid medical science of all the metaphysical excesses
it had accumulated, and retain only those principles with sound empirical
foundations. Helmholtz joined forces with three of Mu¨ ller’s students, Emil du
Bois-Reymond, Ernst Bru¨ cke, and Carl Ludwig; the four, known later as the “1847
group,” pledged their talents and careers to the taskof reshaping physiology into
a physicochemical science.