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J

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

Joe
in folklore, a name for fire.

Jordan sunshine recorder
A sunshine recorder of the type in which the time scale is supplied by the motion of the sun. It consists of two opaque metal semi-cylinders mounted with their curved surfaces facing each other. Each of the semi-cylinders has a short narrow slit in its flat side. Sunlight entering the slits falls on light sensitive paper which lines the curved side of the semi-cylinder. One semi-cylinder covers morning hours, the other afternoon hours.

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

K

Katabatic wind
Any wind blowing down an incline. If warm, it is a foehn. If cold, it may be a fall wind or a gravity wind.

Katathermometer
A type of cooling-power anemometer based upon the principle that the time constant of a thermometer is a function of its ventilation.

Kelvin temperature scale
An absolute temperature scale with the ice point of pure water defined as 273.16 K. The size of the degree is the same as on the Celsius scale, and the zero point is absolute zero.

Kew
pattern barometer-Mercurial barometer with a fixed scale and cistern and which therefore requires only one adjustment before each reading.

Kilogram calorie
See calorie.

Koschmieder's law
A basic equation in daytime visual range theory, relating the apparent luminance of a distant black object, the apparent luminance of the background sky above the horizon, and the extinction coefficient of the atmosphere, or the air layer near the ground. Also called airlight formula.

Knot
The unit of speed in the nautical system; one nautical mile per hour. It is equal to 1. 1508 statute miles per hour or 0.5144 meters per second.

Konimeter
An instrument for determining the dust content of a sample of air. Also spelled conimeter.

Koniscope
An instrument which indicates the presence of dust particles in the atmosphere. Also spelled coniscope.

Krypton
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.

Kytoon
A captive balloon used to maintain meteorological equipment aloft at approximately a constant height. The kytoon is streamlined and combines the aerodynamic properties of a balloon and a kite.