Hawthorn's Mechanics' Slide Rule

From the late 18th to the mid-19th centuries, British engineers began to use slide rules. This ivory and silver instrument is a four-fold engineer's rule that unfolds to a length of 24 inches. On half of one side is a slide rule with A and D scales on the base and B and C scales on the slide. The A and D scales seem to run continuously, although the slide only moves on the second six inches of the rule.

The words IRON and ROPE appear several times along the edge of the A scale. Along the edge of the D scale is marked: DESCRIPTION SQUARE CYL[I]ND[ER] GLOBE SQUARE CYL[I]ND[ER] WEIGHT STRAIN WORK INCLIN[E] POLYGON SIDE GOVERNORS H[ORSE]P[OWER] ENGIN[E]S STE[A]M TEM[PERATURE]. When the rule is folded, these markings correspond to the tables on the other half of the instrument.

The other half of this side has a table of gauge points for the A scale. Instructions printed on the rule suggest that calculations on the slide rule were intended to be made with calipers. Additional tables and instructions for working with ropes and chains are on this half, which is marked: IMPROVED & ARRANG[E]D (/) BY R^T HAWTHORN (/) CIVIL ENGINEER (/) NEWCASTLE TYNE.

The other side has a scale of 24 inches divided to eighths of an inch along the edge. The metal joint has a protractor divided in increments of 5 degrees and marked by tens from 0 to 180. When the instrument is folded around the joint, there are tables for the extreme strain possible in bars and beams of various substances and for equivalent measures. The joint is marked: G. R. STEPHENSON (/) ENGINEER (/) Adam Pensom.

In 1832 civil engineer Robert Hawthorn (1796–1867) designed a new form of slide rule for manufacturing locomotives and other engines. In 1859 dealers sold the rule for 5 shillings and 6 pence. The names on the joint may refer to the British civil engineer George Robert Stephenson (1819–1905), nephew to the engineer George Stephenson (1781–1848), who sought mechanical advice from Hawthorn's father, and to Adam Pensom (b. 1824), who was a retired gas engineer living in London, according to the 1881 British census. The Smithsonian acquired this object in 1973.

References: Robert Hawthorn, Instructions for the Use of the Mechanics' Sliding Rule (Newcastle-upon-Tyne, 1841), available online at http://www.physics.uq.edu.au/physics_museum/hawthorne/; "Mr. Robert Hawthorn," Minutes of the Proceedings of the Institution of Civil Engineers 27 (1867–1868): 590–592; advertisement by John Archbutt, The Mechanics' Magazine, n.s., 1, no. 10 (March 4, 1859): 486; Peter M. Hopp, Joint Slide Rules (Jeremy Mills Publishing: Lindley, Huddersfield, West Yorkshire, 2009).

Currently not on view