Impact Figures on Polished Rock Salt Surfaces


IF a small steel ball is dropped from a height of a few inches on a polished rock salt surface, the imprint of the ball on the crystal surface remains as a circular depression of one or two millimetres in diameter. The surface is deformed, however, over a region many times the area of the circular depression. If an optical test plane (a piece of ordinary plate-glass will do) is placed on the crystal and the surface examined in monochromatic light, the interference pattern shows a number of families of ‘loops’ extending away from the imprint of the ball.

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SMITH, S. Impact Figures on Polished Rock Salt Surfaces. Nature 127, 855–856 (1931).

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