Ball and ring of 's Gravesande, 1725-1800
Inv V09248

In the construction of railways, in the building of bridges and houses, account is always taken of the expansion of materials. Because when something gets hotter, it also increases slightly in size. The Leiden professor Willem Jacob 's Gravesande devised this gadget in order to demonstrate the effect to his students. The ball is first heated so that it expands to the point where it no longer fits through the ring. Next the ball is placed on the ring, where it continues to cool until it fits in it again. At that moment the ball suddenly drops down without anyone having given it a helping hand!'s Gravesande's intention was to surprise his students so much that they would never forget the experiment. And he succeeded pretty well, since ''s Gravesande's ball and ring' is still one of the best-known demonstration experiments.