Since the late 19th century, the optical microscope had been trapped by an insurmountable physical limit: the wavelength of visible light, formulated by Ernst Abbe, which prevented resolving details below about 200 nanometers, regardless of lens quality. In 1928, at the Technische Hochschule in Berlin, Ernst Ruska, an electrical engineering student, begins researching, under Max Knoll's supervision, how to focus electron beams using short magnetic coils, by analogy with the glass lenses that focus light. On April 7, 1931, Ruska obtains the definitive proof that the principle works: a device with two short magnetic coils in series succeeds in magnifying the image of a metal grid 16 times — too modest to compete with an optical microscope, but enough to demonstrate that it was possible to form magnified images using electrons and magnetic fields instead of light. Knoll and Ruska publish the result in 1932 in the foundational paper "Das Elektronenmikroskop", coining the term that gives the discipline its name. The immediate problem is that electrons generate intense heat that destroys the observed samples, severely limiting the instrument's practical usefulness. Bodo von Borries, also a doctoral student in the same research group, joins the decisive technical design: together with Ruska, he surrounds the magnetic coils with an iron shroud that considerably concentrates and shortens the focal length of the magnetic field — the so-called "pole shoe lens" — jointly patented on March 17, 1932. With this much more efficient lens, Ruska completes his doctoral thesis in August 1933 and, on September 23, 1933, builds a two-stage electron microscope with a magnification of 12,000 times, surpassing for the first time in history the resolution of the best available optical microscope. The Abbe limit, which had seemed a definitive physical barrier, is broken. Despite the technical success, Ruska fails to convince industry to invest in producing the instrument — the problem of sample heating remained unsolved, and the question "who would be the customers for such a device?" discourages potential investors — until, years later, Ruska and von Borries — now brothers-in-law after von Borries married Ruska's sister — convince Siemens in 1937 to found an electron microscopy laboratory, which would launch in 1939 the world's first commercial electron microscope. The technique would later allow, for the first time in human history, observation of individual viruses, cellular organelles, and the structure of materials at atomic scale, opening entire fields of biology, medicine, and materials science previously inaccessible to direct observation.