Circular Protractor

This circular German silver protractor is divided to quarter-degrees and marked by tens from 0° to 350° in the clockwise direction and from 10° to 360° in the counterclockwise direction. The inner edge has indentations at the 0/360, 90/270, 180/180, and 270/90 degree points. A transparent horn center allows positioning on an engineering drawing. A vernier, which may be adjusted with a micrometer screw, permits readings to one minute of accuracy. A clamp screw is adjacent to the micrometer screw. A magnifying glass that may be raised and rotated is screwed to the vernier arm near the center of the protractor. A 6-inch blade extends from the vernier.

Although there is no maker's mark, the protractor is similar to a Gem Union protractor marketed by Dietzgen of Chicago and Stieren of Pittsburgh for $23.50 in the early 20th century. Gem Union was a Dietzgen brand and represented the highest grade of drawing instruments manufactured or sold by Dietzgen. By 1911, every Gem Union instrument was stamped with the Dietzgen monogram. There is no such stamp on this protractor, so it likely either was manufactured earlier or was a copy.

This protractor was apparently used by employees of the Calumet & Hecla Mining Company, which operated highly profitable copper mines in northern Michigan in the late 19th and early 20th centuries. Universal Oil Products (UOP, Inc.; now a division of Honeywell) purchased the company in 1968, while its productivity was declining. The mines closed in 1970, and UOP donated at least three dozen objects, including this one, to the Smithsonian in 1982.

References: Catalogue & Price List of Eugene Dietzgen Co., 7th ed. (Chicago, 1904), 45–49, 191; Catalogue & Price List of Eugene Dietzgen Co., 8th ed. (Chicago, 1907), 47–51, 214; Catalogue & Price List of Eugene Dietzgen Co., 9th ed. (Chicago, 1910), 63–67, 244; Catalogue & Price List of Eugene Dietzgen Co., 12th ed. (Chicago, 1926), 56–57, 204; The Wm. E. Stieren Co., Catalogue and Price List (Pittsburgh, n.d.), 209.

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