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“The vertical section in the direction of the axis of the telescope. The eye-piece ab consists of two planoconvex lenses a, b, of nearly the same focal length, and with the two convex sides facing each other. They are placed at a distance apart less than the focal length of a, so that the wires of the micrometer, which must be distinctly seen are beyond b. The eye-piece slides into the tube cd, which screws into the brass ring ef, through two openings in which the oblong frame, containing the micrometer slides, passes.” —The Encyclopedia Britannica, 1903


The Encyclopedia Britannica, New Warner Edition (New York, NY: The Werner Company, 1893)


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