The Babbage Difference Engines

There are numerous sites on the web documenting Charles Babbage's engines for generating number series.

This is one of the more accessible overviews.

The machine is essentially a set of vertical shafts each carrying multiple stages of toothed gears with the gear wheels of each stage on each shaft intermeshing with the next.

I have not been able to locate a clear schematic visualizing how the turns on each shaft of a certain number of teeth practically translates to computing a number series.

In default of someone more knowledgeable coming up with this, I have created the schematic below.

In 1991 the Science Museum in Kensington, England, built a complete Difference Engine from Babbage's original drawings.

This magnificent machine has many more columns and many more stages than engine No1 but the essential principle of operation must be as I have outlined above.

An identical Engine completed in March 2008 is on display at the Computer History Museum in Mountain View, California until May 2009.