This is an early marine barometer and dates from around 1800. As far back as 1668, when Robert Hooke presented his findings on the matter to the Royal Society, it was thought that the ability to measure air pressure at sea would be advantageous. The problem of the oscillation of the mercury caused by the motion of the ship, however, meant it was to be another century before such a measuring instrument was perfected.

This example has a round mahogany case with a silvered brass scale and a thermometer fitted to the inside of the barometer door. A manual vernier is fitted to the barometer scale to ensure that accurate readings can be taken. It would have been hung from brass gimbals and was weighted to ensure it remained upright on board ship. It is thought to have once belonged to Lord Nelson, being given as a gift to his friend Captain (later Admiral) George Cockburn. Although this provenance is unconfirmed there is certainly an association to support it. Its ownership can be traced to the Nisbets, the family name of Nelson's widow, Frances. Nelson was also known for his generosity and the Museum contains many examples of his gift-giving. It was presented to the Museum in 1950 by the actor, Sir Lewis Casson, a relation by marriage to the Nisbet family.