Chapter 3

Liquid-in-glass Thermometer

A device for measuring temperature that consists of a tube with a liquid-filled bulb at one end. The expansion or contraction of the fluid indicates temperature.

Isotherm

A line connecting points of equal air temperature.

Wind Chill Temperature

A measure of apparent temperature that uses the effects of wind and temperature on the cooling rate of the human body. The wind chill chart translates the cooling power of the atmosphere with the wind to a temperature under nearly calm conditions.

Growing Degree days

A practical application of temperature data for determining the approximate date when crops will be ready for harvest.

Celsius Scale

A temperature scale devised by Anders Celsius in 1742 and used where the metric system is in use. For water at sea level, 0 is designated the ice point and 100 the steam point.

Fahrenheit Scale

A temperature scale devised by Gabriel Daniel Fahrenheit in 1714 and used in the English system. For water at sea level, 32 is designated the ice point and 212 the steam point.

Kelvin (Absolute) Scale

A temperature scale used primarily for scientific purposes and having intervals equivalent to those on the Celsius scale but beginning at absolute zero.

Bimetal Strip

A thermometer consisting of two thin strips of metal welded together, which have widely different coefficients of thermal expansion. When temperature changes, the two metals expand or contract unequally and cause changes in the curvature of the element. Commonly used in thermographs.

Maximum Thermometer

A thermometer that measures the maximum temperature for a given period in time, usually 24 hours. A constriction in the base of the glass tube allows mercury to rise but prevents it from returning to the bulb until the thermometer is shaken or whirled.

Minimum Thermometer

A thermometer that measures the minimum temperature for a given period of time, usually 24 hours. By checking the small dumbbell-shaped index, the minimum temperature can be read.

Annual Mean Temperature

An average of the 12 monthly means.

Thermistor

An electric thermometer consisting of a conductor whose resistance to the flow of current is temperature dependent; commonly used in radiosondes.

Heat Stress Index

An index widely used by the National Weather Service that combines the elements temperature and humidity to establish the degree of comfort or discomfort.

Thermometer

An instrument for measuring temperature; in meteorology, a thermometer is generally used to measure the temperature of the air.

Thermograph

An instrument that continuously records temperature.

Temperature Controls

Any factor that causes temperatures to vary from place to place and from time to time.

Cooling Degree Days

Each degree of temperature of the daily mean above 65 F. The amount of energy required to maintain a certain temperature in a building is proportional to the cooling degree-days total.

Heating Degree Days

Each degree of temperature of the daily mean below 65 F is counted as one heating degree-day. The amount of heat required to maintain a certain temperature in a building is proportional to the heating-degree days total.

Fixed Points

Reference points, such as the steam point and the ice point, used in the construction of temperature scales.

Apparent Temperature

The air temperature perceived by a person

Specific Heat

The amount of heat needed to raise 1 gram of a substance 1 C at sea-level atmospheric pressure.

Temperature Gradient

The amount of temperature change per unit of distance

Monthly Temperature Range

The difference between maximum and minimum temperatures in a month.

Daily Temperature Range

The difference between the maximum and minimum temperatures for a day.

Annual Temperature Range

The difference between the warmest and coldest monthly means.

Daily Mean Temperature

The mean temperature for a day that is determined by averaging the hourly readings or, more commonly, by averaging the maximum and minimum temperatures for a day.

Monthly Mean Temperature

The mean temperature for a month that is calculated by averaging the daily means

Ice Point

The temperature at which ice melts.

Steam Point

The temperature at which water boils.

Absolute Zero

The zero point on the Kelvin temperature scale, representing the temperature at which all molecular motion is presumed to cease