An instrument for measuring angles of inclination. Used in conjunction with a ceiling light to measure cloud height at night.

An instrument whose calibration is determined by comparison with an absolute instrument.

Wind with a speed between 7 and 10 knots (8 and 12 mph), Beaufort scale number 3.

A device attached to a meteorological instrument to provide ventilation; usually a suction fan.

An instrument used to indicate wind direction.

The record of an aneroid barograph.

The direction from which the wind is blowing, measured in points of the compass or in azimuth degrees.

Readily taking up and retaining moisture.

An evaluation, according to set procedures, of those weather elements which are most important for aircraft operations. Always includes cloud height or vertical visibility, sky cover, visibility, obstructions to vision, certain atmospheric phenomena, and ...

A balloon designed to float at a constant pressure level. This may be accomplished by a pressure valve which controls the release of ballast so as to maintain flight above a selected pressure level until the supply of ballast is exhausted. See Moby Dick b ...

A unit of energy equal to 101 ergs or to 0.2389 calories.

An instrument, for the recording of two or more meteorological parameters, in which the ventilation is provided by a suction fan.

A reversing thermometer (for seawater temperature) which is not protected against hydrostatic pressure. The mercury bulb is therefore squeezed, and the amount of mercury broken off on reversal is a function of both temperature and of hydrostatic pressure.

The effect upon the measurement of rainfall caused by the presence of the rain gauge.

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.

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.

A relatively small-scale, upward moving current of air.

The maximum difference in output for any given input (within the specified range) when the value is approached first with increasing, and then with decreasing, input signals. Caused by energy absorption in the elements of the measuring instrument. Usually ...

Same as freezing point.

A thermometer which utilizes the thermal properties of gas. There are two forms of this instrument: (a) a type in which the gas is kept at constant volume, and pressure is the thermometric property, and (b) a type in which the gas is kept at constant pres ...