The elevation of the water surface in a stream as measured by a river gauge with reference to some arbitrarily selected zero datum.

A polariscope consisting of a specially constructed double plate polarizer and a tourmaline plate analyzer. Polarized light passing through the instrument is indicated by the presence of parallel colored fringes, while unpolarized light results in a unifo ...

A line drawn through geographical points having the same duration of sunshine (or other function of solar radiation) during a given interval of time.

Small particle on which water vapor condenses.

An instrument for measuring the extinction coefficient in water.

A type of pressure-plate anemometer in which the plate, restrained by a stiff spring, is held perpendicular to the wind. The wind-activated motion of the plate is measured electrically. The natural frequency of this system can be made high enough so that ...

A mercury barometer arranged so that the position of the upper or lower meniscus may be measured photographically. In one design the image of the meniscus is formed on a rotating drum covered with sensitized paper so that a continuous record of pressure a ...

The play or loose motion in an instrument due to the clearance existing between mechanically contacting parts.

Old snow that has become granular and compacted as a result of melting and refreezing.

A thermometer based upon the principle that the velocity of a sound wave is a function of the temperature of the medium through which it passes. Sonic thermometers possess very short time-constants and eliminate radiation error.

A chronograph used to make a time-record of certain measured meteorological elements. The most common type, the triple register, records wind direction and speed, duration of sunshine, and amount of rainfall (sensed respectively by a contact anemometer, M ...

Operation mode of a communication circuit in which one end can only transmit and the other end can only receive.

Of equal or constant pressure, with respect to either space or time.

An element that can control current without moving parts, heated filaments, or vacuum gaps.

An atmospheric sounding instrument which is supported by a captive balloon and used to obtain temperature and humidity data from the ground level to a height of a few thousand feet. The data is telemetered to the ground through a wire cable.

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 fl ...

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 ...

The process of modifying some characteristic of a wave (the carrier) so that it varies in step with the instantaneous value of another wave (the modulating wave) in order to transmit a message. The modified characteristic may be frequency, phase, and/or a ...

In meteorology, an area of low pressure; a low or trough.

A defective maximum thermometer of the liquid-inglass type in which the mercury flows too freely through the constriction. Such a thermometer will indicate a maximum temperature that is too low.