Goniometers

   The Goniometer was invented by William Hyde Wollaston (1766-1828) {Phil. Mag., 27 (1807). Wallaston’s device was used to measure the angles between the plane surfaces of crystals. "It consisted of a brass circle, graduated on its edge and mounted on one end of a horizontal axis. The crystal to be measured was mounted on the other end of the axis. The observer adjusted the crystal until a distant image was reflected off one of the facets into the observers eye, rotated the crystal until the next surface reflected the same image (the eye being kept stationary), and then read the angle between the two crystal faces from the graduated circle." (From Steven C. Turner, "Goniometer" in Instruments of Science, Robert Bud and Deborah Jean Warner, eds (Garland Publishing, New York, 1998) pp 290-292)
   The instrument at the left, in the collection at the University of Cincinnati, was made by Ph. Pellin of Paris ca. 1900. At the right is a goniometer on display at Transylvania University in Lexington, Kentucky. It was bought from the firm of E.M. Clarke of London in August 1839 for £3 13 6.

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