Mechanics His first important scientific achievement, an 1847 treatise on the
conservation of energy, was written in the context of his medical studies and philosophical background. His work on energy conservation came about while studying
muscle metabolism. He tried to demonstrate that no energy is lost in muscle movement, motivated by the implication that there were no
vital forces necessary to move a muscle. This was a rejection of the speculative tradition of
Naturphilosophie and
vitalism which was at that time a dominant philosophical paradigm in German physiology. He was working against the argument, promoted by some vitalists, that "living force" can power a machine indefinitely. Drawing on the earlier work of
Sadi Carnot,
Benoît Paul Émile Clapeyron and
James Prescott Joule, he postulated a relationship between
mechanics,
heat,
light,
electricity and
magnetism by treating them all as manifestations of a single
force, or
energy in today's terminology. He published his theories in his book
Über die Erhaltung der Kraft (
On the Conservation of Force, 1847). In the 1850s and 60s, building on the publications of
William Thomson, Helmholtz and
William Rankine helped popularize the idea of the
heat death of the universe. In fluid dynamics, Helmholtz made several contributions, including
Helmholtz's theorems for vortex dynamics in inviscid fluids. File:Helmholtz-1.jpg|1889 copy of Helmholtz's "Über die Erhaltung der Kraft", no. 1 File:Helmholtz-2.jpg|Title page of "Über die Erhaltung der Kraft", no. 1 File:Helmholtz-3.jpg|First page of "Über die Erhaltung der Kraft", no. 1
Sensory physiology Helmholtz was a pioneer in the scientific study of human vision and audition. Inspired by
psychophysics, he was interested in the relationships between measurable physical stimuli and their correspondent human perceptions. For example, the amplitude of a sound wave can be varied, causing the sound to appear louder or softer, but a linear step in sound pressure amplitude does not result in a linear step in perceived loudness. The physical sound needs to be increased exponentially in order for equal steps to seem linear, a fact that is used in current electronic devices to control volume. Helmholtz paved the way in experimental studies on the relationship between the physical energy (physics) and its appreciation (psychology), with the goal in mind to develop "psychophysical laws". The sensory physiology of Helmholtz was the basis of the work of
Wilhelm Wundt, Helmholtz's student, who is considered one of the founders of experimental
psychology. More explicitly than Helmholtz, Wundt described his research as a form of empirical philosophy and as a study of the mind as something separate. Helmholtz had, in his early repudiation of
Naturphilosophie, stressed the importance of
materialism, and was focusing more on the unity of "mind" and body.
Ophthalmic optics In 1851, Helmholtz revolutionized the field of
ophthalmology with the invention of the
ophthalmoscope; an instrument used to examine the inside of the
human eye. This made him world-famous overnight. Helmholtz's interests at that time were increasingly focused on the physiology of the senses. His main publication, titled
Handbuch der Physiologischen Optik (
Handbook of Physiological Optics or
Treatise on Physiological Optics; English translation of the 3rd volume here), provided empirical theories on
depth perception,
colour vision, and
motion perception, and became the fundamental reference work in his field during the second half of the nineteenth century. In the third and final volume, published in 1867, Helmholtz described the importance of
unconscious inferences for perception. The
Handbuch was first translated into English under the editorship of
James P. C. Southall on behalf of the
Optical Society of America in 1924–5. His theory of
accommodation went unchallenged until the final decade of the 20th century. Helmholtz continued to work for several decades on several editions of the handbook, frequently updating his work because of his dispute with
Ewald Hering who held opposite views on spatial and colour vision. This dispute divided the discipline of physiology during the second half of the 1800s.
Nerve physiology In 1849, while at Königsberg, Helmholtz measured the speed at which the signal is carried along a nerve fibre. At that time most people believed that nerve signals passed along nerves immeasurably fast. He used a recently dissected sciatic nerve of a frog and the calf muscle to which it attached. He used a
galvanometer as a sensitive timing device, attaching a mirror to the needle to reflect a light beam across the room to a scale which gave much greater sensitivity. transmission speeds in the range of 24.6 – 38.4 meters per second. Helmholtz showed that different combinations of resonators could mimic
vowel sounds:
Alexander Graham Bell in particular was interested in this but, not being able to read German, misconstrued Helmholtz's diagrams as meaning that Helmholtz had transmitted multiple frequencies by wire—which would allow multiplexing of telegraph signals—whereas, in reality, electrical power was used only to keep the resonators in motion. Bell failed to reproduce what he thought Helmholtz had done but later said that, had he been able to read German, he would not have gone on to invent the telephone on the
harmonic telegraph principle. The translation by
Alexander J. Ellis was first published in 1875 (the first English edition was from the 1870 third German edition; Ellis's second English edition from the 1877 fourth German edition was published in 1885; the 1895 and 1912 third and fourth English editions were reprints of the second).
Electromagnetism Helmholtz studied electrical oscillations from 1869 to 1871, and in a lecture delivered to the Naturhistorisch-medizinischen Verein zu Heidelberg (Natural History and Medical Association of Heidelberg) on 30 April 1869, titled
On Electrical Oscillations, he indicated that the perceptible damped electrical oscillations in a coil connected to a
Leyden jar were about second in duration. In 1871, Helmholtz moved from Heidelberg to Berlin to become a professor of physics. He became interested in
electromagnetism, and the
Helmholtz equation is named for him. Although he made no major contributions to this field, his student
Heinrich Rudolf Hertz became famous as the first to demonstrate
electromagnetic radiation.
Oliver Heaviside criticised Helmholtz's electromagnetic theory because it allowed the existence of
longitudinal waves. Based on work on
Maxwell's equations, Heaviside pronounced that longitudinal waves could not exist in a vacuum or a homogeneous medium. Heaviside did not note, however, that longitudinal electromagnetic waves can exist at a boundary or in an enclosed space. ==Philosophy==