Slide RulesCylindrical Slide Rules
Writing a logarithmic scale in a spiral that is then imprinted around the outside of a cylinder allows instrument makers to lengthen the scale. Since a logarithmic scale only needs to run to 10 twice to include all possible results from adding or subtracting two logarithmic numbers, this means that the distance between the points on the scale may be increased. When any two numbers on the scale are further apart, the user may read a fractional position between these numbers (expressed as a decimal) to a finer level of granularity. For example, on a 10" linear slide rule, results generally may be calculated to only three significant figures (0.123, 1.23, 12.3, 123, 1230, and so on). A cylindrical slide rule may provide results of up to seven significant digits (0.1234567, 1.234567, 12.34567, 123.4567, 1234.567, and so on).
On the other hand, cylindrical slide rules were typically about twice as expensive to produce as linear slide rules, and the provenances for the objects on this page indeed suggest that, in the main, only corporate and government offices could afford them. A number of the objects in this category were received with instruction manuals and advertising pamphlets, which may be viewed in the Index by Makers & Retailers. The collection includes multiple examples for several of the objects, as the 23 items below represent only eight different slide rules, half developed in Europe and half invented by Americans. The cylindrical slide rule by Edwin Thacher, a Pennsylvania railroad bridge designer, also illustrates the 19th-century shift in production from Europe to the United States, as originally William Ford Stanley's London firm made the entire instrument. Then, Keuffel and Esser of New York City began constructing the wooden drum and brass and wood stand while continuing to import the scales printed on paper and pasted around the drum. Finally, K&E developed its own dividing engine for printing the scales and henceforth manufactured the entire instrument in the United States.
"Slide Rules - Cylindrical Slide Rules" showing 1 items.
- In the mid-19th century, the expansion and regulation of American insurance companies created a need for numerous computations and a demand for instruments to assist in this process. Elizur Wright (1804–1885), one of the first insurance commissioners of Massachusetts, invented this large cylindrical slide rule, patented it in 1869, and sold it to insurance companies for $500.00. It is the equivalent of a linear slide rule more than 60 feet long.
- The instrument consists of two adjacent cylindrical brass drums, each covered with paper and mounted horizontally in a round brass frame, which is screwed to a round wooden base. Two indentations in the side of the base assist with lifting the instrument. A crossbar attached to the frame extends across the length of the drums. Two indicators slide across a groove in the bar. A brass handle with an ivory knob on the right side of the frame rotates the drums. An ivory button on the left side of the frame operates a brake. When the button is locked in a vertical position, the two drums turn together. When the button is horizontal, only the right drum turns.
- The two cylinders are marked identically. Each drum has a spiral of 20 turns, divided logarithmically (perhaps by pencil), with printed numbers to the right of each division. The first digit of a number is read from the crossbar, and the remaining three are printed on the drum. The markings include every digit from 0 to 3,000; every even digit from 3,000 to 6,000; and every other even digit from 6,000 to 10,000. The arithmeter arrived in a badly scratched wooden case that has two metal handles and a keyhole (but no key).
- A metal plaque screwed to the base is marked: No 6 (/) ELIZUR WRIGHT'S (/) ARITHMETER (/) PATENTED AUG. 17TH 1869. (/) N.E.M.L.INS. CO. The New England Mutual Life Insurance Company (now New England Financial), a company with a long connection to Wright and his family, donated this example, one of ten known surviving arithmeters. Wright's son, Walter C. Wright, was the firm's chief actuary from 1866 to 1900. Wright was also a well-known abolitionist. Although this example cannot be definitively credited to him, Joseph W. Fowle, a Boston machinist who invented a rotating rock drill, is known to have built some arithmeters for Wright.
- References: Elizur Wright, "Calculator" (U.S. Patent 93,849 issued August 17, 1869); Peggy A. Kidwell, "Elizur Wright's Arithmeter. An Early American Spiral Slide Rule," Rittenhouse 4 (1989): 1–4; Lawrence B. Goodheart, Abolitionist, Actuary, Atheist: Elizur Wright and the Reform Impulse (Kent, Ohio: The Kent State University Press, 1990), 149, 168; Naom Maggor, "Politics of Property: Urban Democracy in the Age of Capital, Boston 1865-1900" (Ph.D. diss., Harvard University, 2010).
- Currently not on view
- date made
- Wright, Elizur
- ID Number
- catalog number
- accession number
- Data Source
- National Museum of American History, Kenneth E. Behring Center