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Demonstration Slide Rule
Keuffel & Esser Co.
N.Y.
Humboldt S-T-C, c. 1927
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- Usage/History: 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.).
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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.
The catalog description is from the 1933 K&E Educational Products Catalog. The scan is from Clark McCoy's K&E Catalogs site (2005).
Description: The slide rule is made of wood with white
enamel on the front surfaces; it is unfinished on the sides,
ends, and back. The rule is 84 1/2" long x 7 5/8 inches
high by 1 1/2 inch thick. There are four one inch finger holes
in the slider to allow the demonstrator to slide it relative
to the other scales. All divisions, numbers etc. are in black
enamel with the exception of the CI scale whose numbers are in
red. KEUFFEL & ESSER CO. N.Y is printed in bold 1" letters
in the center of the top portion of the rule, while to the left
in 1/4" letters is written: PAT. JUNE 5, 1900, and to the
right, again in 1/4" letters is: MADE IN U.S.A. and MODEL
100. The original cursor window (cellulose nitrate? with an engraved
line filled with black paint) fragmented and has been replaced
with clear acrylic. An eyebolt is attached to the top of the
rule above each end of the A scale. A Chem Dept decal is on the
top, front of the rule above "24" on the A scale. An
oval brass tag, attached with brass pins to the right end of
the rule, is stamped: HUMBOLDT S-T-C / 2094.
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- Research: 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].
Two highly recommended recent books, by Hopp and by von Jerierski, covering the complete history of the slide rule through its effective demise with the development of personal calculators, may be found on the reference list.
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- © R. Paselk
- Last modified 15 September 2005
- All photographs © R. Paselk
