Difference Engine
More info
- Creator
- Charles Babbage
- Released
- Designed 1822, abandoned 1842
- Type
- Mechanical calculator
- Successor
- Analytical Engine
A machine of brass gears that could compute mathematical tables using nothing but addition — and still consumed the largest research grant in Victorian Britain without ever being finished.
The idea rests on the method of finite differences: any polynomial can be tabulated by repeated addition alone, provided you start from the right values. Babbage saw in 1822 that a machine could therefore replace the humans who computed navigation and astronomy tables by hand, and more importantly replace their mistakes. The design handled seven orders of difference at twenty-digit precision and stamped its results straight into a printing plate, so that no typesetter could introduce fresh errors.
The British government put in over £17,000 — roughly the price of two steam locomotives — before cancelling in 1842, twenty years in and with no working machine. The causes were split between manufacturing tolerances, a dispute with chief engineer Joseph Clement over who owned the tooling, and Babbage losing interest once he had a better idea.
Note what it is not: a calculator with no conditional branching, capable of exactly one thing. That limitation is what the Analytical Engine was meant to escape. London's Science Museum built Difference Engine No. 2 from Babbage's drawings in 1991, using only tolerances available in his own century. It worked first time.