IN 1948 JAMES HILLIER, THE RCA PHYSICIST LARGELY responsible for developing the first commercial electron microscope in America, summarized the progress that had keen made and the challenges that lay ahead in mapping the microscopic world using electrons. In a speech to the members of the American Association for the Advancement of Science, he asked his listeners to perform a thought experiment. Suppose, he said, a scientist wanted to examine an entire plant or animal under an electron microscope. “He would soon find that he would not live long enough to complete his work,” Hillier said. It would take 40 years to get a fast glance at the structures in one square inch of the surface of his sample; to photograph the same square inch at the highest magnification thrn available would require 6,000 years. Millier and a colleague had themselves made 40,000 photographic exposures over 9 years, at an average magnification of 10,000 times. “We now realize,” he told his audience, “that in this time we have photographed only one square millimeter of our world.”

But what a square millimeter it was. The electron microscope had allowed biologists to glimpse for the first time the inner structures of the cell, to measure the size of a virus, and to watch bactcriophages—single-cell organisms that attack invading bacteria—in operation. Metallurgists could now see the treacherous peaks and chasms of a smooth-to-the-touch metal surface, and chemists could measure the invisibly small carbon-black particles that mysteriously added strength to automobile rires. All this from an instrument that hadn’t existed before 1931 and that most scientists had believed would prove useless.

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