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Message: <blockquote data-quote="Llew" data-source="post: 952286" data-attributes="member: 175007">We had one when I was young in the '40s. Ours were two birds 'drinking' from one receptacle, each alternately dipping. Glass tubes moulded in the shape of birds, pivoted in the middle. The bottom of the glass was a bulb filled with a liquid which expanded due to the ambient temperature (usually on a windowsill), and travelled up the tube causing the bird's head at the top to drop down.Somehow they dropped back again after a while and repeated the excercise, but can't remember exactly how.Not perpetual motion, just heating and cooling.</blockquote>