Any one of six gases, helium, neon, argon, krypton, xenon, and radon, all of whose shells of planetary electrons contain stable numbers of electrons such that the atoms are chemically inactive.

A clock-driven instrument mounting which automatically and continuously points in the direction of the sun. It is used with a pyrheliometera,hen continuous direct solar radiation measurements are required.

A type of electrical thermometer in which the thermal element is a substance whose electrical resistance varies with the temperature. Such thermometers can be made with very short time constants and are capable of highly accurate measurements.

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

Emission or transfer of energy in the form of electromagnetic waves or particles.

A graphical representation of stage or discharge at a point on a stream as a function of time.

A type of anemometer in which the rotation of an element serves to measure the wind. Rotation anemometers are divided into two classes; those in which the axis of rotation is horizontal, such as the windmill anemometer, and those in which the axis of rota ...

A decrease in the central pressure of a pressure system. Usually applied to a low rather than to a high.

A colloquial term in western Australia for a squall, associated with thunder, on the northwest coast in summer.

The array of indicating marks and figure in relation to which the position of an index is observed, i.e. a scale plate on a recorder.

The volume of liquid water evaporated per unit area in unit time. usually measured as the depth of liquid water lost per unit time from the whole area.

An inert gas. A colorless, monatomic element which is found to occur in dry air to the extent of only 0.000524 percent by volume. Helium is very light, having a molecular weight of only 4.003 and specific gravity referred to air of 0.138. Because helium i ...

Any sudden and heavy rain, almost always of the shower type.

Either of two colored luminous spots that appear at points 22

A device, similar to a potometer, for measuring transpiration, consisting of a vessel containing soil in which one or more plants are rooted and sealed so that water can escape only by transpiration from the plant.

The actual lifting force of an inflated balloon, usually expressed in grams.

A device used on certain types of instruments to prevent unwanted radiation from affecting the measurement of a quantity. Also called solar radiation shield.

The distance or length of flow of the air past a point during a given interval of time.

An instrument for determining the direction of cloud motion. There are two basic designs of nephoscope, the directvision nephoscope and the mirror nephoscope.

A recording magnetometer.