Pair of Hinged Parallel Rules Sold by Keuffel & Esser

One rule is 24" long and is held together by corroded brass hinges. The blades may be solid ebony. Small metal buttons in the center of each blade assist with positioning the instrument. This rule has no identifying markings.

The second rule is 18" long and is held together by nickel plated brass hinges. The blades are made of ebonized boxwood. Two metal knobs at the center of each blade are used to position the instrument. On the left of the knob on the top blade is marked: KEUFFEL & ESSER CO (/) N.Y. Below the knob is marked: 1784. On the right of the knob is marked: TRADEMARK (below the K&E lion logo). The bottom blade is marked: PAT. JUNE 1, 1915.

By 1880 Keuffel & Esser of New York imported ebony parallel rules with brass hinges and positioning buttons, selling the 24" size as model 706 for $2.00. By 1890 the firm was also making its own version of the rules, since the imported wood, which was often grown in Africa, warped and shrank in the climate of the United States. The imported rules were sold as model numbers 1790 (6", 35¢) through 1795 (24", $1.75). K&E stopped selling imported ebony rules in 1909. Rules manufactured at the company's factory in Hoboken, N.J., from hardwoods stained black were sold as model numbers 1780 through 1785. The 18" model 1784 was priced at $1.25 in 1890 and $1.50 in 1913. The company discontinued this product line after 1936, when model 1784 sold for $2.50.

The first rule thus dates to between 1880 and 1909. Charles Christ Pfeiffer (b. 1874) received the patent mentioned on the second rule, for replacing one of the rivets securing one of the hinges with an adjustable screw. He emigrated from Germany as a child and worked as a cabinetmaker and foreman in Hoboken, possibly for K&E since he assigned the patent to the company. In the 1920s Pfeiffer moved to New London, Conn., where he purchased a farm in the 1930s. The second rule dates to between 1915 and 1936.

References: Catalogue of Keuffel & Esser Co., 13th ed. (New York, 1880), 115; Catalogue of Keuffel & Esser Co., 21st ed. (New York, 1890), 133; Catalogue of Keuffel & Esser Co., 33rd ed. (New York, 1909), 201, 223; Catalogue of Keuffel & Esser Co., 34th ed. (New York, 1913), 197; Catalogue and Price List of Keuffel & Esser Co., 36th ed. (New York, 1921), 144; Catalogue of Keuffel & Esser Co., 38th ed. (New York, 1936), 228; Charles C. Pfeiffer, "Parallel Ruler" (U.S. Patent 1,141,483 issued June 1, 1915); 1900–1940 U.S. Census records; World War I Draft Registration Cards, 1917–1918.

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