Charles Babbage - Difference Engine

Difference Engine

In Babbage's time, numerical tables were calculated by humans who were called 'computers', meaning "one who computes", much as a conductor is "one who conducts". At Cambridge, he saw the high error-rate of this human-driven process and started his life's work of trying to calculate the tables mechanically. He began in 1822 with what he called the difference engine, made to compute values of polynomial functions. Unlike similar efforts of the time, Babbage's difference engine was created to calculate a series of values automatically. By using the method of finite differences, it was possible to avoid the need for multiplication and division.

At the beginning of the 1820s, Babbage worked on a prototype of his first difference engine. Some parts of it still survive in the Museum of the History of Science in Oxford. This prototype evolved into the "first difference engine." It remained unfinished and the finished portion is located at the Science Museum in London. This first difference engine would have been composed of around 25,000 parts, weigh fifteen tons (13,600 kg), and would have been 8 ft (2.4 m) tall. Although Babbage received ample funding for the project, it was never completed. He later designed an improved version,"Difference Engine No. 2", which was not constructed until 1989–91, using his plans and 19th century manufacturing tolerances. It performed its first calculation at the London Science Museum returning results to 31 digits, far more than the average modern pocket calculator.