Electron microscope experiments conducted by L. L. Marton of the National Bureau of Standards have developed an electron optical analogy to the Schlieren effect for the quantitative study of electrostatic or magnetic fields. By forming a dark field image of magnetic or electric fields occurring between the electron source and a magnetic lens, a visual representation of fringe fields from the small domains of spontaneous magnetization in ferromagnetic materials is obtained. The characteristics of such field intensity patterns may then be used to compute the field distribution in the region under study. Extension of the principle provides a means of broadening present knowledge concerning space‐charge fields, fields produced by contact potentials, wave guide problems, and the microstructure of metals.

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