# Slipsticks

## Historic Slide Rules

A display of slide rules drawn from the Scientific Instrument Collection of the Macleay Museum

Slide rules became obsolete very rapidly in the early 1970s with the introduction of hand-held electronic calculators. Invented in the seventeenth century, an increasing variety of slide rules was developed during the eighteenth and nineteenth centuries. Many of these had special purposes. By the late nineteenth century, standardised forms of slide rule became the essential working tool of engineers and scientists.

Other calculating devices began to become available - mechanical, and electro-mechanical calculators - and by the 1940s electronic computers were beginning to be built. In the 1970s the electronics revolution made pocket calculators with diverse scientific functions available for very modest prices. The age of the slide rule came rapidly to an end.

With the rise of the ubiquitous desk-top computer there has been an increasing interest in antique calculating devices. Old slide rules are now collector’s items. This display shows a number of types of slide rule, including some early and very unusual examples.

## Logarithmic Scales

The Scottish clergyman and mathematician, John Napier (1550-1617), discovered the principle of logarithms. This enabled calculation involving multiplication and division to be carried out by the addition or subtraction of logarithms. Napier published his discovery in 1614 and published tables of logarithms in 1617.

Edmund Gunter (1581-1626) laid out numbers in a line on a logarithmic scale. This single scale laid out on a wooden strip was an invaluable aid to calculation for surveyors and seamen. Using a pair of dividers (or compasses) a length from one part of the scale could be marked on another part of the scale to carry out the calculation. This had the disadvantage that the points of the dividers soon damaged the fine markings of the scale. The idea then occurred to place the same scale on two separate pieces of wood so that one could be slid against the other.

The full conception of the slide rule in which all the components are held together is attributed to William Oughtred (1574-1660) about 1630.

## First Patent Slide Rule

In the 18th century a great variety of slides rules were developed, with up to four sliders. Possibly the most complicated slide rule of the period was this model invented by John Saxspeach or Suxspeach. It was patented in 1753 and made by Benjamin Parker.

The rule carries two sliders, one on either side, each of which has a brass insert. By combining these together the instrument can be used as a protractor or level. The hollow octagonal slider was probably intended to be used as a telescope although it has no optical fittings. The numerous scales would be useful in surveying, calculating the volume of barrels, making astronomical and calendrical calculations and so on. A few other examples of this slide rule are known.

The Catholic Organon, or Universal Sliding Foot Rule
Invented by John Suxspeach and patented in 1753
Made by Benjamin Parker, London, 1753
MM 86/009

## Engineer’s Slide Rule

This folding engineer’s rule incorporates a slide rule with logarithmic scales for multiplication and division. It also bears several useful tables. It was designed in 1805 by J. Routledge of England following Coggeshall’s pattern of slide rule.

Coggeshall-type slide rule
Made by Edward Preston & Sons, Birmingham, c. 1870
MM 94/026

## Class Room Slide Rule

Large slide rules such as the one at the back of this case were produced for teaching the use of the instrument in class rooms. This one shows the multiplication of two times three on the C and D scales. The answer is marked by the cursor.

This slide rule was made in the New South Wales Department of Education Furniture Workshop Annexe in Balmain about 1970 and supplied to the Sydney Teachers College in 1974, just in time to be obsolete.

Demonstration Slide Rule
Transferred from Teaching and Curriculum Studies, Faculty of Education
MM 98/009

## X-Ray Slide Rule

Following the announcement of Conrad Röntgen’s discovery of X-rays at the beginning of 1896, the technique was repeated in many parts of the world in the next few months. X-rays were very soon applied to diagnostic examination of medical problems such as fractured bones and the location of foreign bodies such as pins or bullets lodged within a person. Early X-ray techniques involved many variables that were difficult to control. This form of slide rule was developed in 1912 in order to guide radiographers for more predictable results, taking into account the distance from the X-ray emitter to the photographic plate (top of stock), the thickness of the part of the body and the strength of the X-ray tube (top slider), the current in the tube and the size of the person (lower slider). The appropriate exposure time was then read off the bottom part of the stock. This is believed to be the earliest form of slide rule for X-ray exposure calculations. A number of other forms were developed in subsequent years.

(For more information on this and other similar slide rules, see J.E. Burns, 'Radiographic exposure slide rules', The British Journal of Radiology, 72 (1999), 48-54)

Retailed in London by Schall & Son, c. 1914
MM 77/004

## Circular Slide Rules

Drawing slide rule scales around a circle enabled a more compact instrument to be produced. A circular slide rule with a 3-inch diameter can provide a 10-inch scale. Nevertheless, circular slide rules were never very popular. There could be problems of parallax in reading the scales but for their size they could be surprisingly accurate.

A variety of circular slides rules were manufactured by Concise in Japan. These were often supplied with a firm’s name on for use as promotional give-aways.

Concise circular slide rule, model no. 300
Made by Concise, Japan, c. 1960
MM 90/012

## Cylindrical Slide Rules

By taking a line and wrapping it around a cylinder a long scale could be made very compact. The most famous cylindrical slide rule is that designed by George Fuller, Professor of Engineering at Queen’s College Belfast. His design was patented in 1878 and continued in production until the 1970s. Its scale is 500 inches (41 feet 8 inches) long with 7250 divisions. This enabled a much greater accuracy than the standard 10 inch slide rule.

This is the uncommon type 2B Fuller with trigonometrical and logarithm scales on the inner cylinder. A number of other types of cylindrical slide rule were produced in the 20th century including the Otis King.

Fuller Cylindrical Calculator, number 9301
Made by Stanley, London, in 1948
Transferred from Department of Geology and Geophysics
MM 82/067

## ‘Modern’ Slide Rules

These are three examples of slide rules used in the 20th century.

10-inch slide rule
The standard size slide rule, this was made by the leading Japanese firm founded in 1895. The use of bamboo was initially introduced by the Japanese for its cost saving, but its lightness and strength soon made it a very desirable material for making slide rules. The ‘SUN’ trade mark was registered in 1917.
Made by Hemmi, Japan, c. 1955, model no. 259D
MM 93/002

50-cm slide rule
The longer scale enabled more accurate calculations to be made.
Made by Faber Castell, Germany, c. 1958
MM 92/007

5-inch slide rule
The convenience of portability at the expense of accuracy.
Made by Keuffel and Esser, United States, c. 1960
MM 96/064

Visit the Oughtred Society website.