Swift Instruments Barometer

This is a barometer, an instrument for measuring atmospheric pressure. There are two main types of barometers: mercury barometers, which measure pressure based on how much force is exerted by the atmosphere on a column of mercury, and aneroid barometers, which operate by mechanically attaching the indicator needle to a vacuum capsule which expands or contracts based on ambient atmospheric pressure. This instrument is most likely an aneroid barometer. This particular instrument, Swift's "Scientist" model, has precision down to the millibar level and was manufactured in France before being imported into the US.