Sexton's Omnimetre Circular Slide Rule

This paper circular rule consists of two paper discs, a celluloid indicator, and a metal screw that holds everything together. Going out from the center of the rotating discs, there are scales of versed sines [3 yellow circles labeled from 3 to 80 degrees—the versed sine of an angle x is (1 - sin x)], the fifth power of N (5 white circles labeled from 1 to 9.5), tangents (3 yellow circles labeled from 5 degrees through 84 degrees), N cubed (three white circles labeled from 1 through 9.5), sines (two circles labeled from 6 to 84 degrees), N squared (two circles labeled from 1 to 95), secants (one yellow circle labeled from 10 degrees to 84 degrees), and a logarithmic B scale running from 1 to 10. On the base disc is a logarithmic A scale, running from 1 to 10, and an equally divided scale for finding logarithms that runs from 0 to 10. THoles in the base make it easier to rotate the disc.

The base disc is marked around the edge: SEXTON'S OMNIMETRE; COPYRIGHT IN THE UNITED STATES 1896. ENTERED AT STATIONERS HALL LONDON FOR INTERNATIONAL COPYRIGHT 1896; NUMERI MUNDUM REGUNT; ENTERED ACCORDING TO ACT OF THE PARLIAMENT OF CANADA IN THE YEAR 1896 BY THADDEUS NORRIS, ENLARGED AND REVISED EDITION. The smaller disc is marked near the center: ALL RIGHTS RESERVED (/) PATENT 1895 U.S. CANADA & EUROPE. The back of the instrument is engraved: THEO. ALTENEDER & SONS (/) PHILADELPHIA. DANKERS is handwritten near the center of the back.

Albert Sexton was a resident of Philadelphia who, according to his own account, read a lecture delivered by Colman Sellers at the Franklin Institute on 20 May 1891. Although the subject of the lecture was the utilization of the power of Niagara Falls, Sellers also mentioned the advantages of the slide rule. Intrigued by these comments, Sexton began to acquire slide rules. He concluded that a less expensive, more complete instrument was needed, and he designed one. When he provided samples to gentlemen visiting a local steam engine manufacturer, Southwark Foundry and Machine Company, he found they were most interested. Arthur Marichal, a Belgian civil engineer, wrote on his sample “Sexton’s Omnimetre” and added the Latin phrase “Numeri Mundum Regunt.” Sexton adopted both the name and the motto.

With the assistance of Philadelphia resident Thaddeus Norris, Sexton introduced several versions of his instrument, including the most complete form, which is represented by this object. Sexton (and Norris posthumously) received the John Scott Medal of the Franklin Institute on 4 January 1899. The instrument was manufactured by the Philadelphia firm of Theodore Alteneder & Sons. The different forms sold for $1.00 to $3.00 around 1900, and this version sold for $4.00 by 1940.

The donor acquired this example in 1938, when he joined the U.S. Navy’s Preliminary Ship Design Branch. He used it in the design of ships from PT boats to aircraft carriers, until his retirement in 1968.

References: Peggy A. Kidwell, "Computing Devices, Mathematics Education and Mathematics: Sexton's Omnimetre in Its Time," Historia Mathematica 36 (2009): 395–404; Thaddeus Norris, "Marker for Slide-Rules" (U.S. Patent 540,184 issued May 28, 1895).

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