Accession No

2252

Brief Description

slide rule, by Cary, English, 19th Century

Origin

England; London

Maker

Cary

Class

calculating

Earliest Date

1800

Latest Date

1900

Inscription Date

Material

ivory; metal (brass); paper (card); hide (leather)

Dimensions

length 306mm; breadth 24mm; thickness 12mm

Special Collection

Provenance

Purchased from Turner and Devereux, London, 07/1976. Purchased with assistance a Grant-in-Aid administered through the Science Museum (PRISM).

Inscription

‘CARY * LONDON’ (obverse)

Description Notes

Ivory slide rule with brass studs.
Obverse: three identical scales, one on the upper stock, two on the slide, marked A, B and C, divided 1 - 10[0], numbered 1, 2...1[0], 2[0]...10[0]. Lower part of stock carries single radius log scale marked D, divided 1 - 10, numbered by 1. Reverse of slide carries sine scale divided [40´] - [90˚], numbered 1, 2...10, 20...70; tan scale divided [40´] - 45˚, numbered 1, 2...10, 20, 30, 40, 45; scale of equal numbers divided [0] - 10, numbered by 1, subdivided to 0.02. Underneath slide is scale marked ‘H’ and ‘present worth annuity’, divided 2 - 100 years, numbered 2, 3...10, 15, 20, 25, 30, 40, 50, 60, 70, 100.
Reverse: upper part of stock carries scale marked A, as that on obverse. slide carries two triple radius log scales, marked E, divided 1 - 100[0], numbered 1, 2...1[0], 2[0]...10[0], 2[00]...100[0]. Lower part of stock carries two scales: upper marked ‘G’ and ‘comp. interest’, ‘principal’ and ‘years amount’, divided 0 - 80, numbered by 10, subdivided to 1; lower divided [0] - 100, numbered by 10, subdivided to 1.
On reverse of slide two scales: upper divided [1.44] - [144], numbered 2, 3...1[0], 2[0]...10[0]; lower divided in inches [12] - 24, number by 1, subdivided to 1/8. Underneath slide two scales marked ‘F’: first for ‘amount’, divided 2 - 10, numbered by 1; second for ‘annuity forborn’, divided [11] - 80, numbered by 5, subdivided to 1.
One edge: inch scale divided [0] - 12, numbered by 1, subdivided to 1/8.
Other edge: various tables for calculating equal densities of various solids and liquids.
Leather-covered card slip case (one end missing).

Condition good; complete.

References

Events

Description
Developed during the seventeenth century, the modern slide rule is based upon the design by William Oughtred (circa 1630). It is one of many calculation devices that is based on the logarithmic scale, a calculation method invented in 1614 by John Napier.

Before the rise of the pocket electronic calculator in the 1970s, the slide rule was the most common tool for calculation used in science and engineering. It was used for multiplication and division, and in some cases also for ‘scientific’ functions like trigonometry, roots and logs, but not usually for addition and subtraction.

A logarithm transforms the operations of multiplication and division to addition and subtraction according to the rules log(xy) = log(x) + log(y) and log(x/y) = log(x) - log(y). The slide rule places movable logarithmic scales side by side so that the logarithms of two numbers can be easily added or subtracted from one another. This much simplifies the alternative process of looking up logs in a table, thus greatly simplifying otherwise challenging multiplications and divisions. To multiply, for example, you place the start of the second scale at the log of the first number you are multiplying, then find the log of the second number you are multiplying on the second scale, and see what number it is next to on the first scale.

FM:42525