Babbage Difference Engine (Replica)

Part of a difference calculation machine

1821

In 1821, Charles Babbage (1791 - 1871), an English mathematician, began planning a difference engine for creating mathematical tables of functions using differences. These tables were to be used for advantageous inter- and extrapolation of function values and for checking faulty logarithmic tables. The theory underlying the difference engine is based on the mathematical theorem that the nth differences of a polynomial of degree n are constant. If the nth difference of a function is known, further function values can only be determined by addition. In 1832 the mechanic Joseph Clement, who was commissioned by Babbage, succeeded in completing a section of the first Difference Engine consisting of about 2000 individual parts. The original fragment, which is now in the Science Museum in London and of which the Arithmeum owns this exact replica, consists of four columns with cogwheels arranged one above the other and five number rollers each bearing an inscription from 0 to 9. One of the columns forms the result work, in which the functional values are formed. The other three columns show the first, second and third difference. A small part serves as a revolution counter. It is driven by a crank mounted on the top of the cover plate. However, this fragment should remain the only result of Babbage's efforts to create a difference machine. Using the improved design of the Difference Engine No.2, the Science Museum built a functional construction in 1991 based on the sketch material that had been handed down.