Vesels for demonstrating the hydrostatic paradox, 1752.
© Science Museum / Science & Society Picture Library
These were used by the famous scientific lecturer Dr Stephen Demainbray (1710-1782) to show the 'hydrostatic paradox' - basically the same demonstration as the 19th century 'Pascal's vases'. The vesels were filled with water. A balance beam was suspended above the apparatus with one arm carrying a piston which could move vertically in the container, and the other carrying a counter-balance weight in a scale-pan. The presure on the piston in all three vesels was found to be the same, since presure is dependent on depth and not on the volume of water present.