An Early Slide Rule

Abstract

DE MORGAN, in article “Slide Rule” in the Penny Cyclopaedia, points out that though Gunter first used a logarithmic scale, the real inventor of the logarithmic slide was Oughtred. “In the year 1630 he showed it to his pupil, William Forster, who obtained his consent to translate and publish his own description of the instrument, and rules for using it. This was done under the following title, ‘The Circles of Proportion and the Horizontal Instrument,’ London, 1632; followed in 1633, by an ‘Addition, etc.,’ with an appendix having title, ‘The Declaration of the two Rulers for Calculation.’” After referring to a republication of this work in 1660, he goes on:—“The next writer whom we can find is Seth Partridge, in a ‘Description, etc., of the Double Scale of Proportion,’ London, 1685. He studiously conceals Oughtred's name; the rulers of the latter were separate, and made to keep together in sliding by the hand; perhaps Partridge considered the invention his own, in right of one ruler sliding between two others kept together by bits of brass.”