Trigonometric Calculating Instrument

This metal device displays values of trigonometric functions, particularly those encountered in mine surveying. The semi-circular protractor, graduated from 0 to 180 degrees and subdivided to fifteen minutes of arc, slides along an outer radius of a much larger quadrant of a circle. The radius of the circle is divided and a vernier on the base of the protractor allows on to place the protractor exactly to 1/1000 of an inch. A second, adjustable radius extends from the center to the rim of the quadrant, and includes a vernier along it such that it may be measured to 1/1000 of an inch. The rim of the quadrant is also subdivided. With the help of a vernier at the end of the adjustable radius, angles may be read along the rim of the quadrant to 5 minutes of arc. The instrument also includes a metal piece perpendicular to the base of the quadrant that has divisions marked on it and slides along a chord parallel to the base. A flat metal pointer graduated on both sides fits into a vernier attachment that, in turn, fits on the arc of the protractor. Related documentation has numbers 317954.02 through 315954.07.

According to the donor, this is an invention of Frank A. (Francis Asbury) Crampton and his brother Theodore H. M. Crampton prior to 1918. Born in New York in 1888, F. A. Crampton was variously a hobo, hard rock miner, surveyor, assayer, and mining engineer in the western United States. T. H. M. Crampton, born in 1890, was a mining and metallurgical engineer trained at the Colorado School of Mines. Theodore H. M. Crampton of Santa Monica, California, applied for a patent for a “triangle computing and drafting instrument” July 5, 1917. It closely resembles this instrument. The patent was granted (to him alone) on April 9, 1918.

For a related photograph, which mentions Frank Crampton as co-inventor of the calculating instrument, see MA.317954.02.

References:

Accession file.

Frank A. Crampton, Deep Enough: A Working Stiff in the Western Mine Camps, Denver: Sage Books, 1956. This volume does not mention the calculating instrument. A related exhibit did include it (see MA.317954.02).

T. H. M. Crampton, “Triangle Computing and Drafting Instrument,” U.S. Patent 1,262,023, April 9, 1918.

“Theodore H. M. Crampton,” Who’s Who in Engineering 1922-1923, New York: John W. Leonard Corp., 1922, p. 315.

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