Gilson Atlas Calculator Circular Slide Rule

This 10-inch, one-sided aluminum circular slide rule is on a square base coated with plastic. The outer ring of the rule is a C scale divided logarithmically from 1.0 to 10. Inside the ring is a spiral of 30 coils, divided logarithmically from 100 to 1,000, and the equivalent of a C scale 50 feet long. The outer edge of the coil has 30 markings on it, indicating the number of the coil on the spiral that corresponds to a given segment of the scale on the outer ring.

Two transparent celluloid cursors rotate both separately and together. For instance, to multiply two numbers, the longer cursor is set at the index point on the outer ring and the shorter cursor is set at the first number. Then, the longer cursor is moved to the second number, carrying the shorter cursor to the product. The process can be repeated with the numbers on the coils to provide an answer with five significant digits.

The rule is marked near the center: THE (/) ATLAS CALCULATOR (/) PATENTED 1-17-1922. (/) TAVELLA SALES CO. (/) 25 W. Broadway, (/) New York. The Atlas was designed by George W. Richardson, who sold his business to Clair Amasa Gilson in 1919. Gilson received a patent for improving the design in 1922. The instrument was then manufactured by the Gilson Slide Rule Company, which moved from Niles, Michigan, to Stuart, Florida, in 1927. Gilson typically did not mark its rules with the company name or instrument model. Several American instrument dealers retailed Gilson instruments; the Tavella Sales Company distributed not only the Atlas but the TASCO adder (1986.0663.01). Tavella sold the Atlas for $7.50 around 1931.

The instrument has a black imitation leather folding case. It was received with instructions, which are in the accession file. See also 1979.0816.01, 1989.0832.01, and 1998.0119.01.

References: Clair A. Gilson, "Mechanical Calculating Device," (U.S. Patent 1,404,019 issued January 17, 1922); Henry Aldinger and Ed Chamberlain, "Gilson Slide Rules," Journal of the Oughtred Society 9, no. 1 (2000): 48–60 and 9, no. 2 (2000): 47–58; Eugene Dietzgen Company, Slide Rule Manual: Instructions for Using the Atlas Slide Rule (Chicago, n.d.), http://sliderulemuseum.com/Manuals/M216_Gilson_Atlas_Manual_Dietzgen1797A.pdf; The Slide Rule Manual: Instructions for Using the Midget Slide Rule (New York: Tavella Sales Co., [about 1931]), 12, http://sliderulemuseum.com/Manuals/M15_MidgetBinarySlideRuleManual_refC03.pdf; George W. Richardson and J. J. Clark, The Slide Rule Simplified, 7th ed. (Scranton, Pennsylvania: Technical Supply Company, 1918), 98.

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