The machine was built by the Science Museum to original designs dating from between 1847 and 1849. The engine was completed in 1991, the bicentennial year of Babbage's birth. The set of original design drawings consists of twenty main views and a small number of derivative tracings.
During the 1980s, Allan Bromley, an associate professor at the University of Sydney, Australia, studied Babbage's original drawings for the Difference and Analytical Engines at the Science Museum library in London. This work lead the Science Museum to construct a working difference engine No. 2 from 1989 to 1991, under Doron Swade, the then Curator of Computing. This was to celebrate the 200th anniversary of Babbage's birth.
He believed construction would take three years, but 1830 arrived and construction was still not completed.
This was partly due to a serious of personal tragedies occurring in Babbage's life during 1827. The year would see his wife, Georgiana, his father and two of his children all die, and Babbage himself would fall into ill health - a series of events that would see work on the project to cease until the end of 1828.
What Babbage did not, or was unwilling to, recognize was that the government was interested in economically produced tables, not the engine itself. The other issue that undermined the government’s confidence in the difference engine was Babbage had moved on to an analytical engine. By developing something better, Babbage had rendered the difference engine useless in the eyes of the government.
Babbage went on to design his much more general analytical engine, but later produced an improved "Difference Engine No. 2" design, between 1847 and 1849. Babbage was able to take advantage of ideas developed for the analytical engine to make the new difference engine calculate more quickly while using fewer parts.
The Difference Engine was more than a simple calculator, however. It mechanized not just a single calculation but a whole series of calculations on a number of variables to solve a complex problem. It went far beyond calculators in other ways as well. Like modern computers, the Difference Engine had storage—that is, a place where data could be held temporarily for later processing—and it was designed to stamp its output into soft metal, which could later be used to produce a printing plate.
As a founding member of the Royal Astronomical Society, Babbage had seen a clear need to design and build a mechanical device that could automate long, tedious astronomical calculations. He began by writing a letter in 1822 to Sir Humphry Davy, president of the Royal Society, about the possibility of automating the construction of mathematical tables—specifically, logarithm tables for use in navigation. He then wrote a paper, “On the Theoretical Principles of the Machinery for Calculating Tables,” which he read to the society later that year. (It won the Royal Society’s first Gold Medal in 1823.)
Charles Babbage was born on December 26th (most likely in 1791 - reports vary somewhat) in London, the son of a banker. Although a sickly child, his father's money would ensure he received good schooling, gaining admittance to Cambridge University where he would initially attend Trinity College before transferring to Peterhouse, from where he would receive an honorary degree without examination.
Difference engines are so called because of the mathematical principle on which they are based, namely, the method of finite differences. In general, calculating the value of a polynomial can require any or all of addition, subtraction, multiplication and division.
An advantage of the method of finite differences is that it eliminates the need for multiplication and division, and allows the values of a polynomial to be calculated using simple addition only. Adding two numbers using gearwheels is easier to implement than multiplication or division and so the method simplifies an otherwise complex mechanism.
Difference Engine, an early calculating machine, verging on being the first computer, designed and partially built during the 1820s and ’30s by Charles Babbage.