Hermann von Helmholtz has been called a genius in the field of medicine, but the German physician only entered the field because a career in physics didn't seem likely to pay the bills. His greatest discoveries involved the physiology of sight, sound and nerve impulses. Helmholtz, who was born on this date in 1821, helped push the field of ophthalmology ahead when he invented the ophthalmoscope and became the first person to see inside the living human eye. He also added to the work of English ophthalmologist Thomas Young on color vision, now known as the Young-Helmholz theory. Later in his career, Helmholtz finally became a physicist and discovered the first law of thermodynamics.

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