Babbage designed the Difference Engine in 1822 and the Analytical Engine in 1837. Neither was finished in his lifetime. The Science Museum built Difference Engine No. 2 in 1991, and again with its printer in 2002, to prove that Babbage was right and his backers were wrong.
Charles Babbage 1791–1871 · Cambridge, London
Lucasian Professor of Mathematics at Cambridge; mathematician, mechanical engineer, inventor of cow-catchers and ophthalmoscopes; founder, with Herschel and Peacock, of the Analytical Society that brought Leibniz's calculus notation into British practice. Spent forty years trying to build a mechanical computer.
"I wish to God these calculations had been executed by steam."
— Babbage, on finding errors in published tables, 1821
Difference Engine No. 1 1822 commissioned
The Treasury funds Babbage £17,000 — about £2 million today — to build a calculating engine for the Nautical Almanac. Joseph Clement, master engineer, takes seven years to build the calculating section. Babbage keeps redesigning. He and Clement fall out in 1833 over ownership of the tools. The Treasury cuts him off in 1842. The partial machine, a marvel of Victorian precision, goes into storage. It still works.
Ada Lovelace 1815–1852
Daughter of Lord Byron, tutored in mathematics by Mary Somerville and Augustus De Morgan. She translates Menabrea's Sketch of the Analytical Engine from French in 1843 and adds her own Notes — three times the length of the original. Note G contains the first published algorithm: a deck of cards for the Analytical Engine to compute Bernoulli numbers. She also writes the line that becomes the founding metaphor of computer science:
"The Analytical Engine weaves algebraic patterns just as the Jacquard loom weaves flowers and leaves."
Difference Engine No. 2 1849 designed
Babbage's improved second design — simpler, more reliable, 31-digit precision, with a printer attached. He never builds it. The drawings sit in his notebooks. He dies in 1871, frustrated, leaving Mathematical Tables of His Own Calculation as his consolation.
The Science Museum builds 1985–1991, 2002
Doron Swade, curator at the Science Museum London, decides for the Babbage bicentenary in 1991 to build Difference Engine No. 2 to Babbage's original drawings — using only the precision available to a Victorian workshop. The calculating section is completed in 1991 and operates correctly. The full machine with its printer is completed in 2002 and runs in front of audiences in London and at the Computer History Museum in Mountain View. Both machines work. Babbage's mathematics and tolerances were sound; what failed him was money, patronage, and a Treasury that lost patience.
Plan 28 2010–present
The ongoing project to build the Analytical Engine — Babbage's general-purpose machine, the one Lovelace wrote programs for. John Graham-Cumming and the team at Plan 28 are cataloguing Babbage's notebooks digitally, deciding which design state to build, raising funds. If they succeed, Lovelace's Bernoulli-numbers algorithm will run, 180 years late, on the machine it was written for.
Designed in 1822. Built in 1991. Some ideas have to wait for the world to catch up to them.
Sources: Babbage, Passages from the Life of a Philosopher (1864); Swade, The Difference Engine (2001); Bromley, Charles Babbage's Difference Engine No. 2 (1990); plan28.org. Full list at docs/sources.md.