Babbage Difference Engines
A mechanical calculator designed to print mathematical tables without human arithmetic errors, never completed in Babbage's lifetime and built from his plans in 1991.
Charles Babbage proposed the Difference Engine in 1822 to compute tables by the method of finite differences, which needs only addition. A working portion of Difference Engine No. 1 was assembled in 1832 with the engineer Joseph Clement. Government funding ended in 1842 and the full machine was never built.
Babbage later drew a simpler and more capable Difference Engine No. 2 in 1847 to 1849. The Science Museum in London built it from those drawings between 1985 and 1991 for the bicentenary of Babbage's birth, and added the printing mechanism in 2002. It worked as designed, which showed that the design was sound and that Victorian manufacturing could have built it.
Why it matters
The Difference Engines are the best known attempt to automate computation in the 1800s. Babbage's later Analytical Engine added a stored program, a processing unit he called the mill, and a memory he called the store. Ada Lovelace's 1843 notes on that machine are often cited as an early description of programming.
Key facts
- Difference Engine No. 2 has about 8,000 parts and weighs several tons.
- The Science Museum's reconstruction calculates to 31 digits.
- The 1832 demonstration piece is held by the Science Museum, London.
- The Computer History Museum in California displays a second complete No. 2, built for Nathan Myhrvold and finished in 2008.
Sources
- Campbell-Kelly, Martin, and William Aspray, et al. Computer: A History of the Information Machine. 3rd ed. Westview Press, 2013.
- Swade, Doron. The Difference Engine: Charles Babbage and the Quest to Build the First Computer. Viking, 2001.
- Science Museum Group, "Babbage's Difference Engine No. 2" collection pages.