Scofield-Thacher Engineer's Slide Rule

This 22-inch, two-sided wooden slide rule has scales that are printed on paper but not engine-divided. On the front of the base, logarithmic scales are labeled B and C on the left and D and D on the right. The C scale is the inverse of the B scale and is also labeled RECIPROCALS. The first D scale runs from 1 to 3.16, and the second D scale runs from 3.16 to 10. These scales are labeled ROOTS.

Four identical scales are on the slide, all logarithmically divided from 1 to 10 and labeled A. Two of the scales are at the left end of the slide, and two are at the right end of the slide. These scales are also identical to the B scale. Written in pencil on the back of the slide and underneath the slide is the number 1103. The bottom of the base is marked: Patented July 2, 1901.

The back of the base has scales divided logarithmically from 1 to 10 and from 3.16 to 10 to 3.16. These scales are both labeled F at both ends. The slide also has scales divided logarithmically from 1 to 10 and from 3.16 to 10 to 3.16. These scales are both labeled E at both ends. Faded red numbers from 1 to 4 also appear on all four scales. Written in pencil on the back of the slide and underneath the slide is: 1102. The bottom of the base is marked: Patented July 2, 1901.

The top edge of the rule is marked: THE ENGINEERS (/) SLIDE RULE. It is also marked: From E. M. Scofield, Bridge Engineer. (/) Sta. A, – Youngstown, – Ohio. (/) Rule sent prepaid on receipt of price. (/) Factory, – Youngstown, Ohio. The paper pasted on this edge also has the formula ex/f, a description of how to solve this formula with the instrument, and tables of equivalents. The bottom edge of the rule gives seventeen more formulas and instructions. It is marked: DIRECTIONS FOR SCALES A • B • C & D (/) FOR "Op." READ "OPPOSITE" (/) FOR "—" READ "ON SCALE" (/) FOR "Ans." READ "FIND ANSWER" (/) FOR LAST SIX PROBLEMS REVERSE SLIDE.

Edson Mason Scofield (1867–1939) developed this rule in 1891 while he worked for Edwin Thacher (inventor of the cylindrical slide rule bearing his name; see, for example, MA.312866). Thacher applied for a patent on the design in 1900 and assigned a half-interest to Scofield when the patent was issued in 1901. According to the instrument, Scofield may have distributed the rule himself.

It was also sold by Eugene Dietzgen Company of Chicago from about 1901 through at least 1931. The price for model 1787 ranged from $5.00 to $7.00. By 1926 Dietzgen marked the rule with its company name. Meanwhile, Scofield went on to become president and chief engineer of the National Bridge Company of Pittsburgh in 1901. From 1903 he and his brother, Glenn M. Scofield, operated the Scofield Engineering Company in Philadelphia, New York City, and Los Angeles. This example belonged to Robert A. Cummings, a civil engineer who was the father of the donor. Compare to MA.333710.

References: Edwin Thacher, "Slide Rule" (U.S. Patent 677,817 issued July 2, 1901); Catalogue & Price List of Eugene Dietzgen Co., 7th ed. (Chicago, 1904), 173; Catalog of Eugene Dietzgen Co., 12th ed. (Chicago, 1926), 177; Conrad Schure, "The Scofield-Thacher Slide Rule," Journal of the Oughtred Society 3, no. 1 (1994): 20–25; Peter M. Hopp, Slide Rules: Their History, Models, and Makers (Mendham, N.J.: Astragal Press, 1999), 161.

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