Rod Bogart's twitter feed is a blast. Here's his tweet announcing that he's made an hourglass that demonstrates Archimedes’ theorem that the volume of a cylinder is the sum of the volumes of its inscribed sphere and cone: https://twitter.com/RodBogart/status/455123609195802624
@mjd I've seen pictures of this before ... it's fabulous.
The Voronoi diagram of people in the park is pretty neat.
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