Barograph

Part of speech: noun

Definitions

1. A device that records changes in atmospheric pressure over time on a physical medium
2. An apparatus used to provide a continuous tracing of air pressure variations via a mechanical or electronic recording
3. An instrument designed to monitor and graph fluctuations in atmospheric pressure throughout a given period

Etymology: Barograph is a plain compound built from two Greek elements. The first, "baros", means "weight", and in modern science it denotes atmospheric pressure, the weight of the air overhead. The second, "-graph", comes from "graphein", "to write" or "to record", the same root behind "photograph" and "telegraph". Put together, the name describes exactly what the instrument does: it writes down the weight of the air. The device itself follows the same logic. A sealed metal chamber, or a bank of them, expands and contracts as pressure changes, and a pen linked to that movement traces the variation onto a rotating drum wrapped in paper. The result is a continuous line showing how pressure rose and fell over hours or days, which is why the name fits so neatly.