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"The original Merz micrometer of the Cape Observatory, made on Fraunhofer's model. S is the head of the micrometer screw proper, s that of the screw moving the slide to which the so-called "fixed web" is attached, s' that of a screw which moves the eye-piece E. C is the clamp and M the slow motion in position angle, L, L are tubes attached to a larger tube N; the latter fits loosely on a strong hollow cylinder which terminates in the screw V. By this screw the whole apparatus is attached to the telescope." —The Encyclopedia Britannica, 1903

Micrometer

"The original Merz micrometer of the Cape Observatory, made on Fraunhofer's model. S is the head of…