A small pointer extending downward from the top of the cistern of a Fortin barometer. The level of the mercury in the cistern is adjusted so that it just comes in contact with the end of the pointer, thus setting the zero of the barometric scale.

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.

A small, limited-capacity central processing unit contained entirely on one semiconductor chip.

Random Access Memory. The memory of a computer which can be read and written into at any location without passing through preceding locations.

A power supply which achieves its output regulation by means of one or more active power handling devices which are alternately placed in the "off" or "on" states. It is more efficient than linear supplies which vary the conduction of power devices to ach ...

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

Amount of water, expressed as a depth or as a mass, which would be obtained if all the water vapor in a specified column of the atmosphere were condensed and precipitated.

A pointed device which indicates the amount of resistance encountered when it is forced into a material such as snow or soil. See ram penetrometer.

A large plastic constant-level balloon for duration flying at very high altitudes.

The addition of one or more redundant bits to information to verify its accuracy.

A device, similar to a phytometer, for measuring transpiration. It consists of a small vessel containing water and sealed so that the only escape of moisture is by transpiration from a leaf, twig, or small plant with its cut end inserted in the water.

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

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 strong wind characterized by a sudden onset, a duration on the order of minutes, and a rather sudden decrease in speed.

A generic term for any machine that enables a human being to communicate with a computer.

The indicating part of an instrument. For example, the hand of a watch or the meniscus of a mercury column.

An instrument which automatically records the measurement of two or more meteorological elements.

A thermometer designed for use in measuring the temperature of sea water. One form consists of a mercury-in-glass thermometer protected by a perforated metal case. Another form consists of a mercury-in-glass thermometer surrounded by a metal case which fo ...

Readily taking up and retaining moisture.

A hygrometer based upon the diffusion of water vapor through a porous membrane.