An instrument for measuring differences of electric potential.

See wind vane.

A line drawn through geographical points having the same duration of sunshine (or other function of solar radiation) during a given interval of time.

In nautical terminology, a contraction for "weather glass" (a mercury barometer).

A recording hair hygrometer.

See evaporation pan.

General name for an instrument designed to measure the vertical component of the wind speed. See anemoclinometer.

A hypothetical "body" whose surface absorbs no electromagnetic radiation of any wavelength. An idealization exactly opposite to that of the black body. In nature, no true white bodies are known. Moist white pigments exhibiting high reflectivity for visibl ...

A rainbow of angular radius of about 50

A device, similar to a phytometer, for measuring transpiration. It consists of a small vessel containing water and sealed so that the only escape of moisture is by transpiration from a leaf, twig, or small plant with its cut end inserted in the water.

Growth of a cloud or precipitation particle by the collision and union of a frozen particle with a super-cooled water drop.

An instrument which measures the instantaneous rate at which rain is falling on a given surface. Also called a rate-of-rainfall gauge.

A thermometer consisting of a clock mechanism the speed of which is a function of temperature.

Temperarure at which a liquid solidifies under any given set of conditions. It may or may not be the same as the melting point or the more rigidly defined true freezing point or (for water) ice point.

An instrument for the measurement of both solar and terrestrial radiation.

The height at which the maximum wind speed occurs, determined in a winds-aloft observation.

See sea-water thermometer, reversing thermometer.

The general term for anemometers operating on the principle that the heat transfer to air from an object at an elevated temperature is a function of the air speed. Examples are the hot-wire anemometer and the katathermometer.

In a system of moist air, the ratio of the mass of water vapor to the total volume of the system. Usually expressed as grams per cubic meter (g/m3).

A navigational aid used to facilitate the landing of an aircraft at an airport in instrument weather, i.e. low visibility.