Double Barometer and thermometer

Double' barometer and thermometer, c.1 740. This example of a double or folded type, which allows the length of the instrument to be halved, was invented in 1688 and made by Joseph Betali of Paris around 1740. 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 associated with Dr. Stephen Demainbray (1710-1782), a lecturer in experimental philosophy.