Mariners began to use barometers in the 18th century to predict changes in the weather, but it was in the 19th century that their use at sea became widespread. This French marine barometer has a mahogany case and brass fittings, including a suspension ring. Both the barometer and thermometer use mercury and have silvered-brass scales.

The barometer scale is marked 'BAROMETRE MARIN' at the bottom and has two scales - the left-hand scale is headed 'ROCHEFORT' and is marked from 26 to 29, with descriptive terms such as 'VARIABLE' and 'Beau temps' along the scale; the right-hand scale is headed 'GAUTRAU' and is graduated from 70 to 79, with a vernier to allow more accurate reading. The thermometer also has two scales - the left-hand scale is headed 'Centigrade' and is graduated from 0 to 73; the right-scale is headed 'Réaumur' and runs from -10 to 59.