The Difference Engine

Dabeoc Stanley | Lancaster University

The London Science Museum's difference engine, the first one actually built from Babbage's design.
The London Science Museum's difference engine, the first one actually built from Babbage's design.

Hiding on the second floor of the Science Museum in London is an underappreciated mechanical marvel. Intricate and beautiful, with over 8,000 individual cogs, columns, gears, and carriages in gun-metal bronze, it cannot help but draw the curious eye. The Difference Engine No. 2 is a testament to the eccentric genius of Charles Babbage, and a fascinating glimpse of the missed opportunities of a Victorian computer age that never quite was. I have always loved quirky technology, likely as a result of a childhood absorbing the infectious enthusiasm of Fred Dibnah through the television, and volunteering in the workshop at the Isle of Wight Steam Railway. Babbage’s dreams of steam-powered mechanical computing were, therefore, immediately an object of intense personal interest.

The Difference Engine is, essentially, a giant calculator. The concept was first presented by Charles Babbage in a paper given at the Astronomical Society of London in 1822. The idea was to automate the process of solving complex calculations. This job was bedevilling the poor clerks responsible for creating the arithmetic tables underpinning the rapidly industrialising nineteenth-century British economy – individuals known as ‘computers’. A computer’s work was long and tedious, and there was always the risk of errors being introduced.

The Difference Engine was to operate through the calculus of finite differences, breaking down complicated mathematical problems into simple processes like addition and subtraction. The operation is quite simply spellbinding. Each of the eight columns contains thirty-one wheels representing increasing multiples of ten, when the value passes ten the spiral arms whirl and the one is carried up the column in a shimmering mechanical dance. The machine is capable of calculating a result every six seconds and, unlike the poor human computers, automatically prints the results in tables accurate to thirty decimal places. You can watch the Difference Engine in motion here.

Unfortunately for Charles Babbage the Difference Engine No. 2 is not a survivor of the Nineteenth-century, but a lovingly created homage finished in 1991 under the aegis of the Science Museum’s then curator of computing and IT, Doran Swade, drawing upon twenty sheets of the inventor’s unfinished plans from 1847-49. Babbage was brilliant but truculent, and work to complete Difference Engine No. 1 ended in 1833 after he fell out with his chief engineer Joseph Clement over compensation – despite having received £17,470 funding from an understandably frustrated British Government which never received a working prototype. Babbage had grand ambitions of developing a true programmable computer – the Analytic Engine – capable of reading and storing information on Jacquard loom-style punch cards, in much the same manner as a modern-day computer writing to memory. These lofty thoughts never came to fruition.

The tantalising fact, however, is that the Difference Engine No. 2 works. It works despite being constructed to the less precise machining tolerances of Babbage’s own time, and with minimal alterations to his design. To me, this encourages speculation about the road not taken. A mechanical computing revolution in the Victorian era. It might be romantic, but this is what makes the Difference Engine one of my favourite objects.


Dabeoc Stanley is a current History PhD student at Lancaster University. His research is on the eighteenth-century illicit economy, smuggling networks of the Channel Islands and Isle of Man, and the application of GIS in maritime history.