As you might expect from its name, the "Difference Engine" is a strangely difficult object to describe. You might start by imagining the side of a large crib with uprights ringed by small metal wheels — or rather, spools — but it's better to see the thing for yourself.
Well dusted and with all brass fittings polished, it is displayed in the first gallery of the "Information Age" exhibit at the National Museum of American History. Though an amplified voice indicates the machine's importance in the history of science, it rarely draws a crowd. Never doubt, though, that the Difference Engine is a link to high-powered intellectual excitement, and to an astonishing man whom the British government has lately honored with his own postage stamp. He is Charles Babbage, the man who more than 150 years ago first faintly glimpsed today's computer age and strove to reach it.
The Difference Engine is a calculator. It prepares numerical tables using a mathematical technique known as the method of difference. Today such tables — the kind often used in navigation and astronomy — would be computed and stored electronically. Nearly a century and a half ago, the Difference Engine did much the same work, but slowly and mechanically.
Two Swedes, Georg Scheutz and his son, Edvard, built the Smithsonian's machine in 1853. Each of its long shafts holds disks, and each disk has wheels with ten teeth that correspond to marks in the disks. A scientist could set the disks with known figures, odd or even, turn a crank, and by reading down on each shaft, find the result of a calculation. This particular "engine" could also print out its answers. Sold to an observatory in Albany, New York, it was given to the Smithsonian in 1963.
The Scheutzes had no interest in pleasing design. Their device worked well, though, for they had followed to practical completion the concepts of one of the 19th century's most brilliant minds. Inventor and philosopher, Babbage produced a prototype of the original Difference Engine as early as 1822, then kept adding refinements without ever quite finishing it. He enthusiastically endorsed the work of his friends Georg and Edvard Scheutz. But during the years it took them to complete their machine, the inventor's mind was groping toward a mechanical device that would go far beyond calculation. It would actually store the data that it produced, then reuse the information to add more. Babbage described this process as "the engine eating its own tail."
What he foresaw was a primitive computer. As his biographer, Anthony Hyman, wrote, "Babbage worked by himself, far ahead of contemporary thought. He had not only to elaborate the designs but to develop the concepts, the engineering, and even the tools to make the parts. He . . . stands alone: the great ancestral figure of computing."
Charles Babbage was born in 1791 to a Devonshire family of wealth and leisure. He went to a good school, then set out for Cambridge with little inkling of what to expect there except for a warning that it was a bad place to buy wine. Naturally brilliant at math, he found that his mathematics professors actually knew less than he did.
Clearly a genius, Charles appears also to have been a charming young man, filled with a youthful determination to improve math teaching at Cambridge. With his close friend John Herschel, son of the famed astronomer William Herschel, Babbage helped found the Analytical Society.
Like the Lunar Society in the days of Josiah Wedgwood and Erasmus Darwin (grandfather of Charles), two generations before, the "Analyticals" gathered in noisy sociability to discuss, among other things, the manufacture of cloth from cotton and wool, and the iron forges and steel plants then filling England's green Midlands. Their aim was to calculate how science could best support the continuing Industrial Revolution with new techniques, better tools, more accurate planning.
Long before going up to Cambridge, Babbage devised a way to walk on water. "My plan," he wrote, "was to attach to each foot two boards closely connected together by hinges themselves fixed to the sole of the shoe." The thing had worked well enough for young Charles to squish downriver on an ebb tide. But something went wrong, and he had to swim for his life.