For a given locality and month, an empirical expression devised for the purpose of classifying climates numerically on the basis of precipitation and evaporation.

The smallest change in the environment that causes detectable change in the indication of an instrument. Compare to sensitivity.

Electromagnetic radiation lying within the wavelength interval to which the human eye is sensitive, the spectral interval from approximately 0.4 to 0.7 microns (4000 to 7000 angstroms). Bounded on the short-wavelength end by ultraviolet radiation and on t ...

A rain gauge or array of rain gauges designed to measure the inclination and direction of falling rain.

A graduated scale placed in a position so that the stage of a stream may be read directly from it. Staff gauges may be placed on bridge piers or pilings, etc., or placed on specially constructed supports.

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

See photometer.

Wind with a speed between 4 and 6 knots (4 and 7 mph), Beaufort scale number 2.

A motorlike device containing a rotor and a stator and capable of converting an angular position into an electrical signal, or an electrical signal into an angular position. When several synchros are correctly connected, all of the rotors will align thems ...

A thermometer with a muslin-covered bulb which is moistened. used to measure wet-bulb temperature.

A direct-vision nephoscope constructed in the following manner: A grid-work of bars is mounted horizontally on the end of a vertical column and made free to rotate about the vertical axis. The observer rotates the grid and adjusts his or her position unti ...

An instrument, dropped from high attitude and carried by a stable parachute. used to measure the vertical component of turbulence aloft.

Any soft, gentle breeze.

Same as water year.

Same as wind sock.

Wind with a speed between 4 and 27 knots (4 and 31 mph); Beaufort scale numbers 2 through 6.

A hypothetical body which absorbs some constant fraction, between zero and one, of all electromagnetic radiation incident upon it, which fraction is the absorptivity and is independent of wavelength. Compare to black body, white body.

A combination cup anemometer and pressure-plate anemometer, consisting of an array of cups about a vertical axis of rotation, the free rotation of which is restricted by a suitable spring arrangement.

Instrument for measuring the depth to which the soil is frozen.

A type of cyanometer. an instrument used to measure the blueness of the sky. The Linke-scale is simply a set of eight cards of different standardized shades of blue. They are evenly numbered 2 to 26. The odd numbers are used by the observer if he or she j ...