Ten years ago Dr. Clinton Joseph Davisson and his associates at Manhattan's Bell Telephone Laboratories were performing an experiment something like a blind man's investigation of an elephant by the sense of touch. In this case the elephant was a beam of invisible electrons. When Albert Einstein found out what they were doing, he exclaimed: "We stand here before a new property of matter for which the strictly causal theories hitherto in vogue are unable to account."
Research on the atom has attracted some of the most brilliant minds of contemporary science, and atomic history is strewn with the names of Nobel Prizewinners. Aged Sir J. J. Thomson, who discovered the electron, is a Nobelman; so is Niels Bohr of Denmark and so was the late Lord Rutherford of England, who formulated atomic structure. Their atom was, and still is, a nucleus surrounded by electrons. But in the 1920's, with the powerful searchlight of relativity illuminating the atomic field, it became apparent that the picture of the electron as a simple particle of negative electricity—that is, of matter—was not enough. Chicago's Compton (another Nobelman) showed that waves of high-frequency light could behave like particles. In 1924, Prince Louis de Broglie of France enunciated a theory that electrons could manifest themselves as waves.
In Manhattan, Davisson and his colleagues decided to find experimental proof of the de Broglie theory. If a beam of electrons could act like a beam of light, it should show a pattern of concentric rings when diffracted through a crystal. But the low-powered electrons (100 volts) which Davisson was using would not go through a crystal. He knew, however, that a beam reflected from the topmost atoms of the crystal structure would make a pattern similar to that made by a beam passing through. So he decided to explore the recoil pattern of electrons bouncing off the crystal surface.
Fast moving electrons make an impression on a photographic plate as X-rays do, but Davisson's electrons were too slow to obtain such a picture. So he "felt" the pattern of his reflected beam by moving an electron collector around in the recoil region. Connected to an ammeter, the collector translated the strength of the electron beam at a number of points into measured electric current. The pattern having been thus patiently and ingeniously mapped out, it was seen to consist of true diffraction rings. Concluded the researchers: "Our experiments establish the wave nature of moving electrons with the same certainty as the wave nature of X-rays. . . ."
About the same time in Aberdeen, Physicist George Paget Thomson, able son of Sir Joseph John, obtained the same result by a different method. He used much more high-powered electrons, around 50,000 volts. These were able to penetrate the crystalline structure of a film of metal one-millionth of an inch thick. After emerging they were still strong enough to impress a photographic plate, and Thomson obtained the first pictures of diffraction rings created by electrons.