Engines of Our Ingenuity

No. 646:
DIFFERENCE ENGINE NUMBER TWO

by John H. Lienhard

Click here for audio of Episode 646.

Today, more about Ada, Babbage, and a dream realized. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

When Charles Babbage died in 1871, he left a puzzling array of unfinished calculating machines. They fell into two classes -- difference engines and analytical engines. His difference engines were meant to calculate math tables -- logarithms and trig functions. His analytical engines would have been the first computers, if they'd ever been built.

He never finished any of his engines. His funding always ran out. He made only parts of each kind. Worse yet, he wrote little about what he was doing. Lord Byron's daughter Ada did much to explain the class of analytical engines. She published a series of notes about the concept.

It seems pretty clear that the widower Babbage loved Ada. But Ada was married. When she died, still young, from cancer, her mother destroyed any of her correspondence from Babbage. So we're left to guess.

As for Ada, she loved mathematics and betting on horses. She probably loved Babbage as well. She'd learned much of her mathematics from him. She helped preserve his legacy, but she told us only about his analytical engines. What about his difference engines?

A group at the London Science Museum has actually built Babbage's last engine -- his Difference Engine No. 2. It cost a half million dollars, and it weighs three tons.

And it really works. It can calculate numbers to 31 decimal places. That's far more accurate than your pocket calculator. Of course it's much slower. It'd take 22 hours of cranking by hand to get that result. Now the museum is trying to raise another $360,000 to build the printer Babbage designed to go with it.

The museum has used 19th-century materials and technology. Not only did Babbage's mind run a century ahead of its time. Now we see that Babbage really could've built computers with 19th-century resources, if only he could've mustered those resources.

For years we've known about Babbage's so-called Analytical Engine. In fact it was not one engine, but a class of computers. He built parts of his analytical engines just as he built parts of his difference engines.

Ada Byron's notes fixed the Analytical Engine in our minds as a single machine. She left us with a keen sense of unfinished business. But by focusing our vision of Babbage, she also limited it. Now we begin to see that he was even more advanced than we realized. With a little more government funding, he might've changed the course of history.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)


Hyman, A., Charles Babbage: Pioneer of the Computer. Princeton, NJ: Princeton University Press, 1982.

Associated Press, Calculator built from 1849 design works perfectly, scientists say. The Houston Post. Sunday, December 15, 1991, pg. A-51.


The Engines of Our Ingenuity is Copyright © 1988-1997 by John H. Lienhard.

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