SLIDE RULE

a rule consisting of graduated scales capable of relative movement, by means of which simple calculations may be carried out mechanically. In ordinary slide rules these operations include multiplication, division, and extraction of square roots, as well as, in some cases, calculation of trigonometric functions and logarithms. The slide rule remained an essential tool in the mathematics of science and engineering and was widely used in business and industry as well until it was superseded by the portable electronic calculator late in the 20th century. The logarithmic slide rule is a compact device for rapidly performing calculations with limited accuracy. The invention of logarithms in 1614 by the Scottish mathematician John Napier and the computation and publication of tables of logarithms made it possible to effect multiplication and division by the simpler operations of addition and subtraction. Napier's early conception of the importance of simplifying mathematical calculations resulted in his invention of logarithms, and this invention made possible the slide rule. The first known slide rule in which the slide worked between parts of a fixed stock was made by Robert Bissaker in 1654. Others were due to the enterprise of Seth Partridge (1657) and Henry Coggeshall (1677)a slide in a two-foot folding rule adapted to timber measureand Thomas Everard (1683) for gauging purposes. The usefulness of the slide rule for rapid calculation became increasingly recognized, especially in England, during the 18th century, and the instrument was made in considerable numbers, with slight modifications. Improvements in the direction of increased accuracy in graduation were initiated by Matthew Boulton and James Watt from about 1779 in connection with calculations in the design of steam engines at their works at Birmingham, Eng. Amde Mannheim, an officer of the French artillery, invented in 1859 what may be considered the first of the modern slide rules. This rule had scales on one face only, and, although it was quite simple, it was made and designated by his name for more than a century. The Mannheim rule, which also brought into general use a cursor, or indicator, was much used in France, and after about 1880 was imported in large numbers into other countries. In 1814 Peter M. Roget invented his log-log slide rule for performing the involution and evolution of numbers. The fixed scale, instead of being divided logarithmically, is divided into lengths which are proportional to the logarithm of the logarithm of the numbers indicated on the scale; the sliding scale is divided logarithmically. In 1890 William Cox introduced a revolutionary construction providing for scales on both front and back of the slide rule. An indicator with glass on both sides made it possible to refer to all the scales on both sides of the rule simultaneously. Most important of later improvements was the arrangement of the scales, trigonometric and log-log, so that they operate together and at the same time maintain consistent relationship to the basic scales. This arrangement gave added speed and flexibility to the solving of many problems, simple and complex alike, since it produced solutions by continuous operation, without the need of intermediate readings.