I recently saw a puzzle consisting of a glass cylinder, sealed at both ends, that is completely filled with a clear liquid. The cylinder can be stood upright on either end. Suspended in the liquid and at the top, is a small eggtimer. The sand is free to run from the upper part of the hourglass to the lower part, in the usual way. However, the cylinder is too narrow to allow the hourglass to turn around - the only way to turn it the other way up is to turn the whole cylinder over. When this is done, the egg timer is at the bottom but does not float back to the top for some while. Why? That is the puzzle.

Does anyone know whether this can be purchased now, and if so where?

See the link for a full description.

http://www.grand-illusions.com/puzzle.htm

http://scientificsonline.com/product.asp_Q_pn_E_3081980

Does the eggtimer have to be such a tight fit to the cylinder? is the glass a part of this puzzle?

The eggtimer is not in a stable position if the sand is in the top compartment. So he tries to turn around and generates friction which causes him to stay on the bottom. After a while some sand is gone to the lower compartment, the center of gravity is down, no more tilting and no friction. The eggtimer can go up.

Am I right?

Heinz

PS: I think there has to be a rough surface on the eggtimer, and he has to weigh nearly like water.

Sorry, I didn't read the links posted above where my answer is published anyway..

Hi stanalger

Thank you very much for the site link to this puzzle.
Much appreciated.

I have now emailed them to see if they will travel in the post without ending up as a mixture of soggy sand, broken glass and water!