baroscope

Century Dictionary and Cyclopedia

1. n. An instrument used to indicate changes in the pressure of the atmosphere without measuring its absolute weight. See weather-glass and storm-glass.
2. n. A piece of physical apparatus used to demonstrate the upward pressure of the air. It consists of a large body of small density attached to the beam of a balance, and exactly balanced by a small weight. When this is placed under the receiver of an air-pump and the air is exhausted, the arm of the balance to which the large body is attached tips down, since the upward pressure now taken from it is greater than that removed from the small counterpoise.

Wiktionary

1. n. barometer

GNU Webster's 1913

1. n. Any instrument showing the changes in the weight of the atmosphere; also, less appropriately, any instrument that indicates or foreshadows changes of the weather, as a deep vial of liquid holding in suspension some substance which rises and falls with atmospheric changes.