Kern Circular Protractor

Protractors, devices for measuring and drawing angles, were used in professional practice as well as by schoolchildren. The instruments manufactured for surveyors, draftsmen, and the like could be of quite high quality. This circular protractor is one of at least three in the Smithsonian collections that were produced by Kern & Co. of Aarau, Switzerland. Made of German silver, an alloy of 60% copper, 20% nickel, and 20% zinc, it is graduated along the outer edge to one-quarter degree and marked by tens from 0 to 350 in both the clockwise and counter-clockwise directions.

A center cross-plate, which instrument dealers called a "horncentre," contains crosshairs to assist with placing the protractor on a drawing. A movable arm attached to the center contains a vernier scale that allows the user to read angles to one minute of arc. The arm also has a blade-like extension of 3 inches. There are indentions on the interior of the protractor at 0, 90/270, 180, and 270/90 degrees.

Across its diameter, the protractor is engraved: U.S.G.S. No. 8. Stamped on the back of the vernier arm is the number 88. The protractor was purchased by the U.S. Geological Survey between 1879 and 1907, when it was transferred to the Smithsonian. According to the accession record, it was already "badly tarnished" in 1907. Protractors of this style were manufactured by Kern at least as early as 1867. In 1878 and 1881, respectively, the Troy, N.Y., factory of W. & L. E. Gurley, and New York dealer William Y. McAllister sold Kern circular protractors of this size (10" diameter) for $20.00.

See also ID numbers 1977.0460.02 and 1978.2291.01.

References: William Y. McAllister, A Priced and Illustrated Catalogue of Mathematical Instruments . . . Particular Attention is Called to the Swiss Drawing Instruments (Philadelphia, 1867), 23; W. & L. E. Gurley, A Manual of the Principal Instruments Used in American Engineering and Surveying (Troy, N.Y., 1878), 166; William Y. McAllister, A Priced and Illustrated Catalogue of Mathematical Instruments (Philadelphia, 1881), 35.

Currently not on view