Lava Lamp.

My daughter always likes to go to sleep with the lava lamp on. Consequently when it's time for bed we have to do the rounds and make sure all the various lamps are off. I have found myself on the odd occasion stuck there mesmerised for a few minutes before actually turning it off myself. Then, I find I want to watch how long it takes to cool down and stop circulating the lava. Then I find myself wanting to know how long it takes to heat up and start circulating the lava from cold. Yep, it's mesmerising!