Merritt Beam Scale Slide Rule

This paper linear slide rule was designed to assist architects and construction workers with computing the strength of steel beams. There are seven scales: A, safe load in pounds per square foot; B, section of beams; C, spacing of beams in feet; D, span in feet; E, total safe load in net tons; F, manner of loading; G, span in feet. Scales A-B-C-D are meant to be used together, as are scales E-B-F-G. The back of the instrument gives instructions. The instrument fits in an orange paper envelope.
The front of the instrument and the envelope are marked: The Merritt Beam Scale (/) FOR COMPUTING THE STRENGTH OF STEEL BEAMS. They also are both marked: THE JOHN HOWARD HERRICK CO. (/) BALTIMORE, MD., U.S.A. and PRICE ONE DOLLAR. The front of the instrument also is marked: Copyright (/) 1899 (/) by (/) James S. Merritt (/) M.E. and PAT. JULY 1ST, 1902. This last mark refers to a patent for a "slide-scale" taken out on that date by the mechanical engineer James S. Merritt of Philadelphia. The Merritt Beam Scale was mentioned in a textbook as late as 1921.
Although the instrument is named for Merritt, its invention is credited to Edward Wager-Smith (1872–1920), who worked for Merritt & Co. of Philadelphia from 1893 to 1910. See also his Wager Timber Scale (1987.0108.01).
References: James S. Merritt, "Slide Scale" (U.S. Patent 703,437 issued July 1, 1902); "Wager-Smith, E.," National Cyclopaedia of American Biography (New York: James T. White, 1926), xix:136–137; 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
Physical Description
paper (overall material)
metal (part material)
overall: .3 cm x 24.8 cm x 10.2 cm; 1/8 in x 9 3/4 in x 4 1/32 in
place made
United States: Pennsylvania, Philadelphia
ID Number
accession number
catalog number
Rule, Calculating
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Engineering, Building, and Architecture
Slide Rules
Data Source
National Museum of American History, Kenneth E. Behring Center


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