Slide rules are devices used to aid in calculation, and were extremely important tools in science and engineering prior to the development of the hand calculator. Because of their importance instruction in the use of the slide rule was routinely given in Chemistry, Physics, and Engineering classes, frequently using large demonstration rules such as the one seen here. In essence a slide rule works by, 1) adding and subtracting the logarithms of numbers on adjacent sliding scales thereby enabling multiplication and division (log a*b = log a + log b, log a/b = log a - log b), and, 2) comparing various different parallel scales (in essence acting as tables of trigonometric functions, logarithms etc.).

This particular slide rule was the personal property of Dr. John "Jack" B. Russell, Professor of Chemistry at Humboldt (1956-1992). Dr. Russell first used this slide rule as a student in the 1940's, then as a graduate student, and finally as a professor. He gave it to the museum as an example of an instrument which had been used at Humboldt in instruction etc. (11 October 2000).

The idea of using a logarithmic scale for calculations began with Edmund Gunter when he engraved a scale of logarithms on a piece of wood in around 1620 and used a dividers to add and subtract them to or from each other, and thus multiply and divide. In 1632, William Oughtred divised a pair of sliding scales, which when applied to each other could be used to multiply and divide. It wasn't until 1850, however that the modern form of the slide rule, with one rule sliding between two others, and using a sliding cursor, was divised by Lt. Amédée Mannheim. The resulting "Mannheim" slide rule carried the A, B, C, D, S, T, and L scales on a wooden rule. White celluloid was used in slide rules by 1886. In 1887 Keuffel and Esser began the manufacture of slide rules in the U.S. using mahogany with celluloid scales. Before this time slide rules had to be imported. In 1891 the "Duplex" slide rule, carrying folded scales, was divised by William Cox and manufactured by K&E, and by about 1900 the Log Log Trig slide rule took its "final" form.

10" "Polyphase Duplex" slide rule (mahogany & white celluloid), <1934: DF, CF, CIF, C, and D scales on front; K, A, B, S, T, CI, D, and L scales on back. There is a double sided sliding glass cursor held in a metal frame to celluloid sliders. The upper and lower parts of the rule body are led together with nickel-silver brackets riveted to the lower section, and clamped with a screw to the upper. The rule is inscribed(red filled) / PAT. JUNE 5, '00 / DEC. 22.'08 on the front upper (clamped) face and KEUFFEL & ESSER CO. N.Y. on the front lower (riveted) face. KEUFFEL & ESSER CO. is stamped on the upper cursor slider, and PATENT 2,086,502 (for the sliding cursor) is stamped on the lower cursor slider in black. The model number <4088-3> is stamped in red at and parallel to the left end of the slide. There is no serial number. The original leatherette covered cardboard case is included.

The basic history of the slide rule is outlined
in Michael R. Williams, *A History of Computing Technology*,
Prentice-Hall, Inc., 1985, pp. 111-118 and John P. Ellis, *The
Theory and Operation of the Slide Rule*, Dover Pub. Inc., New
York, 1961, pp. 247-250. An extensive history of the slide rule
is found in *A History of the Logarithmic Slide Rule and Allied
Instruments* by Florian Cajori, The Engineering News Publishing
Co., New York (1909) [recently reprinted].The patent number corresponds
to 1937, thus 1937 is the earliest possible date for this rule. Two more recent and excellent treatises are the books by Dieter von Jezierski, *Slide Rules: A Journey Through Three Centurie,* Astragal Press, Mendham (2000), and Peter M. Hopp,* Slide Rules: Their History, Models, and Makers,* Astragal Press, Mendham (1999).

*© R. Paselk**Last modified 28 June 2012*