A Universal Slide Rule? John Suxspeach's 'Catholic organon'

The proliferation of specialist slide rules in the eighteenth century inspired schoolmaster John Suxspeach to create a universal one. This was designed to be used in different disciplines and types of inquiry, and represents an early attempt to enforce universal standards through instrumentation.

These knitted models (Image 1) illustrate the abstract mathematical surfaces that their creator, the Scottish chemist Alexander Crum Brown (1838-1922), describes in an 1885 paper for the Royal Society of Edinburgh.

Models are essential to teaching and research in chemistry. It is useful for students to see an accurate model of a molecule's shape when they are solving a problem. Also, models have been key elements in 20th century chemical discoveries, such as the structure of the DNA molecule. Many types of molecular models exist, each emphasising different information about the molecule.

Why make molecular models?

Models of molecules show the position of the different atoms, more or less to scale and usually with colour coding, and demonstrate how they are bonded together. Chemists don't think that models such as these show what molecules 'really look like'; models are useful tools for visualising the structures and shapes of groups of atoms, which is important in understanding their behaviour. You can feel the shape of the atom groups and investigate how the molecule can move or bend.

Models have been used to represent arrangements of atoms throughout the development of modern atomic theory. The Science Museum in London has wooden models of atoms used by John Dalton (1766-1844) in his lectures. However, it has been suggested that Kepler used models to depict atoms as early as 1611. All of the sets of models in the Whipple Museum date from the 20th century.

Bringing order to the sciences?

As with many mathematical instruments, John Suxspeach's 'Catholic-Organon, or Universal Sliding Foot-Rule' (above) originated as a personal device. Working as a schoolmaster in Stepney, London, he was implored to make the device available to the public, securing the first Royal Patent for a slide rule in 1753.

The device itself was complex. It had a number of scales and carried two sliders, each with brass inserts, which allowed it to be used as a protractor or level. The hollow slider between the two main pieces was probably meant to hold some kind of telescope.

Suxspeach's rule was manufactured by Benjamin Parker and came with an extensive manual. Evidence suggests, however, that it was unsuccessful. Because it was not particularly suited to one purpose, uneducated professionals were not interested in mastering its use. Application-specific rules had scales that were more legible, and their purposes were more readily understood.

Standardising the slide rule

It was not until the 19th century that a true 'standard' slide rule was produced.  Victor Mayer Amédée Mannheim was a student at the École d'Application in Metz, France in 1859, when he came up with his idea for a standardized slide rule for arithmetic calculations. His design was ten inches long and had only four scales, along with a cursor that allowed the user to clearly align numbers.

By the 20th century, precision manufacturing equipment greatly improved the accuracy and consistency of rules produced to this design. Such rules came into wide use as modern engineering and other physical sciences became further established as professions. Whether the increased standardisation of measurement caused or was caused by this broader economic shift is still an open question.