As a medical student from 1838 to
1842, Helmholtz developed his desire
to combine physiology and physics—
an interest he maintained throughout
his life, and one that followed from the
strong influence of his physiology professor, Johannes Müller, and his friendship
with Emil Du Bois-Reymond. At age 21,
Helmholtz earned a doctor’s degree with
his thesis, which described his original
discovery that nerve fibers originate in
ganglion cells. After one year as a resident
at the Charité hospital in Berlin, he joined
the regiment of the royal guards at Potsdam and worked as a military surgeon.
During this time, he also investigated
the heat produced by muscle contraction.
Helmholtz strived to establish a general
law for the conservation of energy that
could be derived from fundamental
From the time he was
a boy, Helmholtz was
encouraged to follow his
curiosity and to cultivate
an appreciation for both
science and the arts.
physical principles. On July 23, 1847,
he presented his accomplishment in a
lecture to the members of the Physical
Society of Berlin: He introduced the
concept of potential energy and derived
the law for the conservation of energy.
He made the assumptions that matter is constituted of mass particles that
[ Helmoltz’s ophthalmoscope ]
Courtesy of American Academy of Ophthalmology Examiner’s eye
Mirror
Correcting lens
Light source
X
interact by central forces (i.e., those
along the lines connecting two particles).
This work propelled him forward in his
academic career.
A year later, he became a teacher of
anatomy at the Academy of Fine Arts
in Berlin and worked as an assistant to
Johannes Müller, a professor of anatomy
and physiology and the director of the
Anatomisches Museum in Berlin. Helmholtz acknowledged that this mentorship
had a major impact on his professional
life. (See sidebar on p. 37.)
After working for a year with Müller,
Helmholtz became an associate professor of physiology at the University of
Königsberg in 1849. He remained there
for the next six years, during which he
continued his studies on nerve physiology
and initiated new investigations into the
fields of physiological optics and acoustics. With a stable academic position, he
married a young woman named Olga von
Velten. His research focused on assessing
the speed of nerve impulses, which at the
time were thought to be so rapid as to
defy measurement. Helmholtz succeeded
in measuring the speed of propagation of
an impulse in frog nerves as 30 m/s.
In the course of his investigations,
Helmholtz developed precision instruments for his physiological and sensory
studies. For his experiments in acoustics, he used an acoustic analyzer that
consisted of a tuned set of spherical
resonators. He also advanced the field
of precision measurements with his use
of techniques for error analysis based on
probability. In addition, he employed
physical models such as eye movements
as demonstration devices.
Subject’s eye
Helmholtz’s invention of the
ophthalmoscope
36 | OPN Optics & Photonics News
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