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At the British Science Museum they have four different models of Charles Babbage’s difference engines (including his designs).

The display implied that he had at least three different designs.

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This surprised me because I only recall reading about two different versions. I saw four different models (one was a partial implementation.)

My question is: Did Charles Babbage design three Difference Engines?

  • This is probably even beyond retro! – tofro Apr 11 '18 at 20:39
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No, there were only two Difference engines. Babbage's son has assembled a demonstration of Engine No. 1, and the Scheutz engine is based on No. 1; however, there could have been variations of the overall design.

The Difference Engine No. 2 existed only in the form of drawings until the Museum has decided to build it.

Babbage has also designed the Analytical engine. Summarizing, he has designed three Engines, two of them Difference, and one Analytical.

  • Ok this is the 4th one - is this v1 or v2? imgur.com/gallery/h7QmX – hawkeye Apr 11 '18 at 23:24
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    @hawkeye It says "Analytical engine trial model" (note the absence of digit wheels), not "Difference engine". The Difference engine No. 2 did borrow some design decisions from the Analytical engine, as mentioned in the Difference engine Wikipedia article: 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. – Leo B. Apr 12 '18 at 0:35
  • It's been a while since I looked into this, so I may have forgotten some of the details, but I believe there were several designs for analytical engines, not just one. – Jules Apr 12 '18 at 9:16
  • @Jules If you mean Initially (1838) it was conceived as a difference engine curved back upon itself, in a generally circular layout, with the long store exiting off to one side. Later drawings (1858) depict a regularized grid layout. from the wikipedia page, that appears to be superficial. In the lectures about Babbage's work that I've attended at the Computer History Museum, this structural detail was not treated as two separate versions of the Analytical engine. – Leo B. Apr 12 '18 at 17:35

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