Philo's thermoscope, c 250 BC.
© Science Museum / Science & Society Picture Library
This apparatus was used in early experiments demonstrating the heating and cooling of matter. When the lead globe is warmed, the air inside expands and pushes its way up the tube, which is immersed in water. If the heat is strong enough, bubbles of air escape. When the globe is cooled, the air contracts and water is drawn back up the tube. Philo was a Byzantine scientist and was probably the first to record the contraction of air in a globe over water when a candle is burnt in it.