Abstract
The study of the structure of matter necessitates methods of investigation utilizing, principally, radiations which may be either undulatory (light, X-rays, ultra-violet or infra-red rays, &c.) or corpuscular (electrons, elementary particles) in character. Among the many techniques now available—of which the best known is that using the ordinary microscope or its recent modification, the phase-contrast microscope—are those using X-rays and the photoelectric effect produced by the impact of these rays upon matter. These relatively new techniques are still not widely known, though they have considerable interest for the metallurgist. The first and most important technique is X-ray micrography, or Microradiography as it is often called; the second, which utilizes secondary electrons, or sometimes other elementary particles, constitutes the technique of Electron Radiography or Microradiography.
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