Orrery based on Ferguson’s “mechanical paradox”

Craft & Design Science
Orrery based on Ferguson’s “mechanical paradox”

Beautiful photographs by Tina Buescher of Jim Donnelly’s orrery based on the mechanism known as “Ferguson’s mechanical paradox.” Good information about the orrery is provided by Ian Coote’s page. As for the “paradox,” well, it boils down to this: the three apparently-identical stacked gears on the end are driven by a single gear, yet move at different rates, which, of course, would be impossible if they were truly identical. News flash: They’re not. But I’m sure it was harder to fight boredom in the 18th century than it is now, and the build is undeniably gorgeous.

8 thoughts on “Orrery based on Ferguson’s “mechanical paradox”

  1. Earl Adams says:

    Want to build one? Plans are in the latest issue of the “Digital Machinist” a Village Press magazine, Page 6. Digital Machinist, The Home Shop Machinist and Machinist’s Workshop magazines are all excellent. I like “The Home Shop Machinist” magazine the best.

  2. jeff-o says:

    Excellent plans on how to make this out of wood can be purchased here:


  3. Jim Horn says:

    Jim is a remarkable fellow – in addition to terrific machining skills he is one of those responsible for the first scientific pocket calculator, the venerable Hewlett Packard HP-35 and many subsequent designs.

    Thank you, Jim, for inspiration on many fronts!

  4. Anonymous says:

    Actually Jim’s calculator work at HP began about a decade after the HP-35 was produced. ;-)

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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