This may be a hard one to describe without a diagram, but I'll try...

Imagine a wall clock. It's circular, maybe 8 inches diameter, with an annulus (yes, that's how you spell the one I'm referring to) about an inch wide for the numbers.

The hands look like normal... but there's no motor in the center making them go round!

The trick is that where the hands cross the inner edge of the clock face, there's a little wire sticking out from the underside of the hand which goes behind the annulus and attaches to one of two concentric rings which are rotating behind the display.

The rings are just big cogs, and they're driven by a tiny motor hidden on the backside of the annulus - invisible from the front.

I've never seen a clock like this but I'm sure you guys will point me at dozens of them, right? :-)

Graham
-- gtoal, Jun 02 2007

Jefferson Clock Co. may be worth a look http://www.clock-museum.co.uk/c160.htm
[Ling, Jun 03 2007]

Others, under the name "Mystery Clocks" http://www.adsw.org...eryClock/index.html
[Ling, Jun 03 2007]

Watches, too http://www.chronoma..._astrographic_3.JPG
[Ling, Jun 03 2007]

On a larger scale http://ircamera.as....images/extcosmo.htm
[pertinax, Jun 03 2007]

See-through gearless clocks have long been Baked (for centuries, actually) by the simple expedient of mounting the hands on glass disks, and rotating the disks from a motor hidden in the stand.
-- DrCurry, Jun 03 2007


This reminds me of Aristotle's trick with concentric spheres (link).
-- pertinax, Jun 03 2007


My suggestion is closest to Ling's "Mystery Clocks" link example of "The Haddon Clock Company".

Similar, but not quite identical as you can build mine without glass. The hand doesn't stop at the ring but would be seen to be floating above it.

I realised after posting that having the minute and hour hand cross would be tricky; I worked out how to do it but it's not as elegant as I first thought. The trick with the hour hand being geared from the minute hand might be better. My illusion falls apart if you can see the back of the clock.

Thanks for the links, you guys are the fount of all knowlege!
-- gtoal, Jun 03 2007



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