Wager Timber Scale Slide Rule

Wager Timber Scale Slide Rule

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Edward Wager-Smith (1872–1920), a native of New Jersey, graduated from the Spring Garden Institute in Philadelphia in 1889 and in 1893 gained employment as a draftsman for Merritt & Company, a structural steel firm in Philadelphia. As he rose to the position of structural engineer by 1910, he invented the Wager Timber Scale and the Merritt Beam Scale (1987.0108.02). This rule assisted architects and construction workers with computing the strength of wooden beams. It has 11 scales: A, thickness in inches; B, depth in inches; C, spacing in feet; D, span in feet; E, fibre [sic] stress in pounds per square inch; F, load in pounds per square foot; G, type of wood; H, depth in inches; I, method of loading; J, span in feet; and K, fibre stress in pounds per square inch. Scales A-B-C-D-E-F are meant to be used together, as are scales A-B-I-J-K-L and scales G-H-I-J.
The back of the instrument gives government recommendations and regulations for safe stresses on wooden beams and a moisture classification chart by A. L. Johnson, "Economical Designing of Timber Trestle Bridges," U.S. Department of Agriculture Division of Forestry Bulletin No. 12 (Washington, D.C.: Government Printing Office, 1902), 11–12. The instrument fits in an orange paper envelope, which has instructions on its flap.
This rule was distributed by the John Howard Herrick Company of Baltimore, a dealer of hardware and building materials. A photographer by avocation, Wager-Smith also designed the Wager Exposure Scale (patented in 1901—see 1993.0386.01) for correctly timing photographic exposures and the Wager Definition Scale (copyright 1905—see 1993.0386.02 and PG*4750) for determining the longest exposure allowable to produce clearly defined images of moving objects.
The instrument is marked on the front and on the envelope: The Wager Timber Scale (/) FOR COMPUTING THE STRENGTH OF WOODEN BEAMS. It is also marked in both places: THE JOHN HOWARD HERRICK CO. (/) BALTIMORE, MD., U.S.A. It is also marked in both places: PRICE ONE DOLLAR. It is also marked on the front: PAT. JULY 1ST, 1902. This refers to a patent for a "slide-scale" resembling the Merritt Beam Scale and issued on that date to James S. Merritt of Philadelphia. The Wager Timber Scale was advertised for sale from Philadelphia by January 1905 and was mentioned in a textbook as late as 1921.
References: "Wager-Smith, E.," National Cyclopaedia of American Biography (New York: James T. White, 1926), xix:136–137; "Notes and Comment," The New Photo-Miniature 6, no. 3 (1904): 558; James S. Merritt, "Slide Scale" (U.S. Patent 703,437 issued July 1, 1902); "The Wager Timber Scale," Municipal Journal and Engineer 18, no. 1 (1905): 48; "Municipal and Technical Literature: New Publications," Municipal Engineering 29, no. 6 (1905): 448–449; Ernst McCullough, Practical Structural Design (New York: U.P.C. Co., 1921), 81.
Currently not on view
Object Name
slide rule
date made
Wager-Smith, Edward
place made
United States: Pennsylvania, Philadelphia
Physical Description
paper (overall material)
metal (part material)
overall:.3 cm x 24.8 cm x.3 cm; 1/8 in x 9 3/4 in x 1/8 in
ID Number
accession number
catalog number
Credit Line
Transfer from Smithsonian Institution Libraries
Rule, Calculating
See more items in
Medicine and Science: Mathematics
Engineering, Building, and Architecture
Science & Mathematics
Slide Rules
Data Source
National Museum of American History
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