Aneroid Barometer

Aneroid barometers measure barometric pressure through mechanical rather than hydraulic means. First investigated in 1795 by Nicolas-Jacques Conté and patented in 1845 by French physicist Lucien Vidie, the basic aneroid barometer does not consist of a glass tube filled with mercury, but instead contains a metal chamber, a coiled spring, a shaft with bar arm, and a gauge calibrated in both inches and millibars. Any increase or decrease in atmospheric pressure causes the thin walls of the chamber—or sylphon, as it is correctly known—to contract or expand respectively. Tightly wound inside the sylphon, the spring in turn reacts by either opening or closing, while rotating the thin shaft and its attached arm to a given point on the dial. From there the current barometric pressure can be noted and its degree of change from its last position observed. Favored by meteorologists, scientists, and mariners because of its portability and ease-of-use, the basic aneroid model remains in widespread use around the world despite longstanding concerns regarding its precision and reliability in certain weather conditions.

More sophisticated aneroid barometers employed by the National Hurricane Center (NHC) and the Joint Typhoon Warning Center (JTWC) are constructed from alloys (such as nickel-silver or silver- brass) to compensate for changes in external temperature and are equipped with digital displays instead of the traditional gauge or dial configuration. Aneroid barometers have also been modified for use in microbarographs and for deployment in hurricane-hunting weather-reconnaissance aircraft such as the SUPERFORTRESS B-29 the NEPTUNE P2V-3W, and the ORION WP-3.