Astonishing Science. Spectacular museum.

The Difference Engine was conceived in 1821 in an effort to mechanise the production of mathematical tables. Unlike the earlier calculators of Schickard, Pascal and Leibniz, the engine was not designed to perform basic arithmetic but to calculate a series of numerical values and automatically print the results. Difference engines were designed to calculate using the `method of finite differences’, a well used principle of the time. The advantage of using the method of differences is that it eliminates the need for multiplication and division in the calculation of a particular class of mathematical functions called polynomials. The Difference Engine only used addition which is easier to mechanise than multiplication and division.

Manufacturing parts for his engines stretched the standards of engineering practice of the time. The intricate shapes required special jigs and tools and the Engines’ mechanisms demanded hundreds of near-identical precision parts. Babbage conceived his Engine designs at a time when production techniques were in transition between craft traditions and mass-production and there was not yet the means of producing repeated parts automatically.

Babbage conducted an extensive survey of manufacturing techniques and practice by visiting manufactures and craft workshops in England and on the Continent. He concluded that the precision and intricacy required for the construction of his Engine were beyond the capabilities of the technology of the day. This study, conducted during the 1820s, formed the basis of his influential book entitled On the Economy of Machinery and Manufactures, published in 1832.

The design specification for the full size Difference Engine No. 1 required an estimated 25,000 parts which would have had a combined weight of some fifteen tonnes. The Engine, if completed would have stood eight feet high, seven feet long and three feet in depth. Babbage hired Joseph Clement, a skilled toolmaker and draughtsman, to build the Engine. This portion of the Difference Engine, 'the finished portion of the unfinished engine', was completed in 1832 and is among the most celebrated icons in the prehistory of computing. It is the oldest surviving automatic calculator and among the finest examples of precision engineering of the time.

Babbage benefited from substantial government funding - £17,500. But work on the Engine was halted in 1833 when Clement downed tools following an unresolved dispute over compensation for moving his workshop four miles to new premises near Babbage’s house.

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