Making a difference

The 19th century origins of the computer

When was the computer invented? Among possible answers to this question, the credit for designing the earliest precursor to modern machines goes to 19th-century British mathematician and engineer Charles Babbage (1791–1871).

Babbage and railways

Babbage took a keen interest in one of the age’s most important developments, the railway. He contributed several inventions and was present at the opening ceremony of the Manchester and Liverpool line, in north-west England on 15 September 1830. The day also saw the death of parliamentarian William Huskisson, who was run over by George Stephenson’s locomotive “Rocket” — the world’s first railway passenger fatality. “I feared... the people madly attempting to stop by their feeble arms the momentum of our enormous train,” wrote Babbage later.

Perhaps the accident spurred Babbage to concern himself with railway safety, as, in 1838, he invented the cowcatcher (also known as a “pilot”) that could be attached to the front of locomotives to clear obstacles from the track. In answer to the question in Pioneers’ Page of December 2007, it is Babbage who connects the cowcatcher with computing.

From human to mechanical computers

Thousands of years ago, the first device to help people manipulate long series of numbers was the abacus. In the 17th century, as the pace of scientific observations increased, the slide rule was invented by Englishman William Oughtred in 1622. The following year Wilhelm Schickard, of Germany, made the first mechanical calculator. Philosopher and mathematician Blaise Pascal came up with the Pascaline in 1645, to help his father’s work in the French tax system. In the 1670s, Gottfried von Leibniz invented a Stepped Reckoner.

There were important reasons for achieving correct figures. Navigation of ships, for example, required precise tables in nautical almanacs to discover a vessel’s position. New inventions aimed not only to make calculating faster; they were also meant to remove the risks of human error.

Such errors greatly annoyed Babbage. In 1821, he and his friend John Herschel (son of the astronomer William Herschel) found numerous faults in tables they were revising for the Royal Astronomical Society. Correcting the tables was painstaking work, leading Babbage to exclaim “I wish to God these calculations could be executed by steam!” He decided to automate a process that, until then, was performed by people called “computers.” In so doing, he took important steps towards creating what we know as computers today.

The Difference Engine

With the aim of reducing labour and guaranteeing accuracy, Babbage’s “Difference Engine” was to comprise thousands of cogs called “figure wheels”. Its name derived from use of the mathematical “method of differences,” by which calculations are achieved through repeated additions of the differences between successive terms in a series. This allows difficult multiplications to be replaced with simple additions. Teeth on each cog stood for numbers, with the wheel at the bottom of a column showing units, the second showing tens, and so on. Babbage constructed a demonstration model of the Difference Engine and announced his invention at the Royal Astronomical Society in 1822.

A revolutionary aspect of the engine was that it was entirely automatic. Previous calculators required each mathematical operation to be entered by hand, and so expertise in arithmetic was needed to achieve a correct result. In contrast, the Difference Engine could be used by anyone. It was the world’s first device to incorporate mathematical rules into mechanisms. “The marvellous pulp and fibre of a brain had been substituted by brass and iron, (Babbage) had taught wheelwork to think,” wrote his biographer Harry Wilmot Buxton.

By 1849, Babbage had designed his more efficient “Difference Engine Number 2.” It was to contain eight columns, each with 31 figure wheels — meaning it could generate a 31-digit calculation. Half the engine’s parts were dedicated to a printer, so that no human hand could introduce mistakes into the results. It not only printed these, but also could be programmed to give various formats (such as the grouping of data sets) to the print-out.

However, aside from partial models, neither version of the Difference Engine was completed. It was left to Swedish inventor Per Georg Scheutz to finish a device in 1853, based on Babbage’s design, which he showed at the Exposition Universelle in Paris in 1855. Then, in 1991, at the Science Museum in London, a full-scale Difference Engine was constructed according to Babbage’s plans. The work was supervised by the museum’s curator of computing, Doron Swade, who later wrote “we had built the first Babbage Engine, complete and working perfectly, 27 days before Babbage’s 200th birthday.”

Advancing further

One reason for Babbage not finishing the Difference Engine was that he turned his attention to creating an even more advanced machine: a general-purpose, programmable computer. This will be the topic of the next Pioneer’s Page.