'Double' barometer and thermometer, c 1740.
© Science Museum / Science & Society Picture Library
Barometers and thermometers were invented in the late 17th century. This example of a double or folded type, which allows the length of the instrument to be halved, was made by Joseph Betali of Paris around 1740, but invented in 1688. The reading was taken from the right-hand tube using the level of a light oil which has now evaporated. The scales on both instruments had not yet been standardised. This instrument is asociated with Dr Stephen Demainbray (1710-1782), a scientific lecturer of the 18th century.