Bras clockwork bell, 1761.
© Science Museum / Science & Society Picture Library
This clockwork bell was made by George Adams, instrument maker to the king. When the bell was placed under a bell jar and set ringing, the noise made by the bell could be heard. If the air was removed from the bell jar using an air pump, the noise made by the bell became fainter. In a container where the air was compresed, the bell remained audible but the strokes of the hammer were slowed down.