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THE DIFFERENCE ENGINE—FACT AND FICTION
CHARLES BABBAGE was a nineteenth century mathematician who recognized the computational drudgery of assembling tables of logarithms, trigonometric and other mathematical functions. This was the Industrial Age, after all. Why couldn’t this drudgery be done by machine?
Charles Babbage (1792-1871), mathematician, polymath.
The first of his attempts, the Difference Engine, was just that: a device dedicated to churning out values for a given mathematical table. Babbage showed a small prototype to the British Astronomical Society in 1822, and members responded by awarding him the Society’s first gold medal.
Then came the challenge of building a full-size version. Over two decades Babbage spent considerable time, £6000 of his own money and another £17,000 in government grants, all to no avail.
This portion of Babbage’s incomplete Difference Engine resides in the Science Museum, London. Images from Calculating Machines and Computers.
The Difference Engine calculated its tables through repeated additions, all performed by a series of interacting gear wheels. One complication was purely that of fabrication, attempting to achieve the necessary close tolerances with machining capabilities of the era.
But another was Babbage’s unbridled enthusiasm for new ideas. The Difference Engine was a one-trick pony, its interacting gears designed for a single calculatory project. Why not, Babbage reasoned, design an engine to perform many different calculations?
He lost interest in the Difference Engine. Two Swedes, Georg and his son Edvard Scheutz, continued its development, and by 1843 they had a working version. In fact, they tried to sell Differences Engines, only to find that any production of mathematical tables was a pretty limited field.
The business model for producing Difference Engines wasn’t a very robust one; here, the Scheutz version.
Babbage was no more successful with his multi-purpose Analytical Engine, though he certainly had his technical ducks lined up correctly. The Analytical Engine was to use punched cards for storing not only the numbers, but also the sequence of operations to be performed. This, of course, is the key idea that separates a computer from a mere calculator.
Calculating Machines and Computers, Shire Album 247, by Geoffrey Tweedale, Shire Publications, 1990. Both Amazon.com and ABEBooks.com list this most informative paperback secondhand.
The idea of punched cards wasn’t Babbage’s. It had been devised by Frenchman Joseph-Marie Jacquard, his purpose to program looms for weaving complex patterns. The pattern was defined by holes in the cards; an opening allowed the warp thread to be employed, lack of one omitted this particular thread at that particular point of fabrication.
The idea evidently worked with threads, but not with Babbage’s Analytical Engine.
At least not in real life. But what would a mid-Victorian world be like, had the Analytical Engine fulfilled its promise?
This is precisely the wonderful premise framing The Difference Engine, by William Gibson and Bruce Sterling. Gibson and Sterling are recognized today for all but inventing the cyberpunk genre. None of us realized it back in 1990 when The Difference Engine came out, but these two were inventing the steampunk movement as well.
This edition of The Difference Engine celebrates the 20th anniversary of its publication.
Would that Charles Babbage had been so successful. ds
© Dennis Simanaitis, SimanaitisSays.com, 2012
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