[Phil]

The early 19^th century British inventor Charles Babbage was a pioneer in attempts to mechanize mathematical computations. He felt that machines could be used to produce and typeset tables of various mathematical numbers so necessary for a modern civilization to function. Existing, hand-calculated and hand-typeset tables were riddled with errors, and this was holding back science, technology, and finance.

Babbage designed (and tried to have built) a Difference Engine to do these calculations, based on the method of finite differences, and requiring only addition to function. Later, he conceived of the Analytical Engine, an extension of Difference Engine No. 2, to actually carry out programs (including looping) using punch cards inspired by those used with Jaquard Looms. Ada, countess of Lovelace, was a mathematician who became the first computer programmer for this unbuilt machine.

• Scientific American, February 1993, Redeeming Charles Babbage's Mechanical Computer. https://www.scientificamerican.com/article/redeeming-charles-babbages-mechanic/ (paywall). This article describes the building of Difference Engine No. 2 for the Science Museum, London, in time for the 1991 bicentenary of Babbage's birth. It worked, but not without some minor fixes to the design, proving his concepts and that it could have been built with the technology of the time.
• https://www.scientificamerican.com/article/150-year-old-computer-babbage/ a slideshow of the Difference Engine.
• https://en.wikipedia.org/wiki/Difference_engine
• https://en.wikipedia.org/wiki/Analytical_engine
• http://www.computerhistory.org/babbage/
• http://www.smithsonianmag.com/history/what-a-difference-the-difference-engine-made-from-charles-babbages-calculator-emerged-todays-computer-109389254/ A brief social history of Babbage.
• http://history-computer.com/Babbage/AnalyticalEngine.html A detailed look at the proposed Analytical Engine.
• https://plan28.org/ Someone is trying to build the Analytical Engine!
• http://www.fourmilab.ch/babbage/

Babbage's designs, although more-or-less functional (errors in the designs may have been deliberate, to prevent industrial espionage), appear to have been near the limit of mid-19^th century machining capabilities. Even if he had received continued funding (funding ended for the Difference Engine, and what had been built was scrapped), it is questionable whether it would have produced something usable. Even the 1991 version built for the Science Museum (London) had to be hand-tweaked to stop jamming and overcome friction.

So…

Charles Babbage attempted to build a decimal, purely mechanical calculating machine. I've always wondered what the world would be like today if he had succeeded (especially with the Analytical Engine), and computing had nearly a century's head start. Given the technology of his day (mechanical, steam power, hydraulic, pneumatic, and electromechanical relays), and the architectural concepts of modern computers (binary handling of numbers, stored and self-modifiable code and data, etc.), what might he have accomplished? It's fun to think of steampunk non-electronic computers nearly two centuries ago.

[Phil]

Just some random thoughts on actually building either a Difference Engine or the (more complex) Analytical Engine. The Science Museum took a huge gamble when they hand-verified the Difference Engine and then built it to see if it would work. They did have some friction problems (requiring a 4:1 gearing down of the hand crank to get enough torque), and were plagued by jamming problems for a while. They needed to do some hand-tuning of certain parts, which were intended to be identical. It could have very easily happened that they built this thing, and couldn't get it to run, proving that Babbage was a foolish dreamer.

Now, at least one group wants to actually build the programmable computer: the Analytical Engine. I would strongly suggest that they do a complete 3D solid model (in a computer) before cutting the first piece of metal. Assume very low friction and no inertia for moving parts, and see if it actually works as expected. Remember, on the Difference Engine, numerous errors and/or deliberate design obfuscations were found and had to be corrected. Once it works in theory, ramp up the friction and inertia to realistic levels, and see how much torque and force will be needed to operate it, and whether the parts will be strong enough. You don't want to spend tens of thousands of hours cutting parts and assembling it, only to have a shaft twist apart because there was too much friction!

In general, are there affordable 3D modeling programs that could be used to emulate any mechanical computer design, and see if it will work before going through a lot of work to actually build it? Kind of ironic isn't it — to use a modern electronic digital computer to verify the design of an early 19^th century mechanical computer!

[Phil]

A nice video on Babbage's work: https://www.computerhistory.org/babbage/