#physics definitions
- Hydrometer — A measuring instrument consisting of a sealed glass tube, equipped at its lower part with a ballast bulb filled with shot or mercury and at its upper part with a thin graduated stem, used for the direct determination of a liquid's density or specific gravity. In a structural sense, its operation is based on variable vertical immersion in the fluid depending on its density, the level to which the stem sinks indicating the desired value on the scale.