A line of equal or constant pressure.

Upwarddirected solar radiation, reflected by the earth's surface and the atmosphere.

An instrument resulting from the combination of a thermograph and a hygrograph and furnishing, on the same chart, simultaneous time recording of ambient temperature and humidity.

An instrument used for measuring geometric angles. See radio direction-finder.

The outer, solid portion of the earth: the crust of the earth.

The greatest distance at which it is just possible to see and recognize with the unaided eye (1) in the daytime, a prominent dark object against the sky at the horizon, and (2) at night, a known, preferably unfocused, moderately intense light source.

Readily taking up and retaining moisture.

A fabric cone attached to a metal ring and used to indicate wind direction. often at airfields.

Instrument which measures and records the amount of evaporation over time.

A thermopile used in some types of radiation instruments. See solarimeter.

Line drawn through geographical points recording equal amounts of precipitation during a given time period or for a particular storm.

Pyrheliometer based on the comparison of the heating of two identical metal strips, one exposed to radiation, the other to a joule effect.

An instrument for recording ocean waves. Most recorders are designed for recording wind waves, that is waves of periods up to about 25 seconds, but some are designed to record waves of longer periods such as tsunamis or tides.

A small, limited-capacity central processing unit contained entirely on one semiconductor chip.

A sunshine recorder of the type in which the time scale is supplied by a chronograph. It consists of two bulbs, one of which is blackened, which communicate through a glass tube of small diameter. The tube is partially filled with mercury and contains two ...

An instrument which measures the effective terrestrial radiation. See Angstrom pyrgeometer.

A mercury barometer in which the lower mercury surface is larger in area than the upper surface. The basic construction of a cistern barometer is as follows: A glass tube one meter in length, sealed at one end is filled with mercury, and then inverted. Th ...

A tube designed to measure the rate of flow of fluids. It consists of a tube having a constriction or throat at its midsection. The difference between the pressure measured at the inlet and at the throat is a function of the fluid velocity. Compare to Pit ...

An inert gas. An element found in the atmosphere to the extent of only 0.000114 percent by volume. Its molecular weight is 83.7.

A system in which radar techniques are used to determine the range, elevation, and azimuth of a radar target carried a!oft by a radiosonde, so that wind data may be obtained along with the other meteorological data.