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Am′i-ci's prism.

A glass prism mounted beneath the stage of a microscope to obliquely illuminate an object beneath the stage. The prism has a flat-bottom side and two lenticular sides, combines the refracting and reflecting powers, and throws a converging pencil of rays upon the object. It has three adjustments: one on a horizontal axis to direct the rays upward at the required angle; one for distance from the axis of the microscope, to vary the obliquity; one by rotation on a vertical axis, to determine the direction whence the rays shall proceed.

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