In the decades after 1850, Hermann von Helmholtz undertook extensive investigations into
the nature of vision and hearing that rested on his deep interest in music and visual art.
His unfolding conception of the “ manifolds ” or “ spaces ” of sensory experience radically
reconfigured and extended Newton ’ s connection between the musical scale and visual
perception via Young ’ s theory of color vision. In the process, Helmholtz ’ s studies of
hearing and seeing led him to compare them as differently structured geometric
manifolds.
Helmholtz ’ s life trajectory, spanning activity and mastery in many fields, was legendary
in his own time. Though deeply interested in physics from early youth, family circum-
stances dictated his initial career as an army surgeon (1843 – 1848). Even while performing
his onerous duties, he completed his seminal essay “ On the Conservation of Energy ”
(1847), which was of great importance in establishing the fundamental status of that prin-
ciple.^1 In his ensuing activities as professor of physiology at K ö nigsberg (1849 – 1855),
Helmholtz undertook an extensive study of many aspects of nerve action, which began
with innovative experimental studies. He succeeded in measuring the velocity of propaga-
tion of nerve impulses (1850), a feat others had doubted was even possible, given the great
celerity of those impulses.^2 To accomplish this, Helmholtz had to invent a myograph that
allowed a frog ’ s muscle to record itself ( figure 14.1 ). This led, later that year, to his general
study of methods of measuring the extremely small time intervals involved in this new
arena of experimental physiology, for which time itself became both an experimental
desideratum and an avenue to the attendant theoretical and philosophical questions to
which he and many others had been alerted by the work of Immanuel Kant.^3 Thus, Helm-
holtz designed his tachistoscope ( figure 14.2 ) to obviate the extraneous effects of eye
movement by illuminating the eye with an extremely short burst of light, giving a nearly
instantaneous image of the eye ’ s position.
The annus mirabilis 1850 also included Helmholtz ’ s most famed optical invention, the
opthalmoscope, still in use today to examine the retina and the fundus of the eye.^4 But
besides this well-known medical instrument, he also introduced many others, including
the opthalmotrope, a mechanical model to demonstrate eye movements ( figure 14.3 ). Such
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