particularly that of the sun. 



Actinometers may be classified, according to 

 the quantities which they measure, in the following 

 manner: (a) PYRHELIOMETER, which measures the inten- 

 sity of direct solar radiation; (b) PYRANOMETER, 

 which measures global radiation (the combined in- 

 tensity of direct solar radiation and diffuse sky 

 radiation); and (c) PYRGEOMETER, which measures the 

 effective terrestrial radiation. (24) 



ACTIVE RUDDER . The Active Rudder has played an 

 important role in improving general maneuverability, 

 maintaining course when a vessel is stopped (which 

 is helpful in taking oceanogiraphic data) and pro- 

 ceeding at high speed in strong winds and high seas. 

 In the Active Rudder a submersible electric motor 

 is installed in a rudder of normal design and a 

 propeller is fitted to the motor shaft at the after 

 end about even with the trailing edge of the rudder. 

 The water filled and water lubricated squirrel cage 

 induction motor may range from 20 to 1600 SHP and 

 is arranged for reverse rotation. Thus by swinging 

 the rudder, thrust may be applied either forward 

 or reverse in the direction of the rudder, similar 

 to the manner of steering a small boat with an out- 

 board motor. (30) 



ACTIVE SONAR . Active sonar is the method or equip- 

 ment by which information concerning a distant 

 object is obtained by evaluation of sound generated 

 by the equipment. (1) 



ACTIVE TRANSDUCER . An active transducer is a 

 transducer whose output waves are dependent upon 

 sources of power, apart from that supplied by any 

 of the actuating waves, which are controlled by 

 one or more of these waves. (1) 



AD . U. S. Navy ship designation for Destroyer 

 Tender. 



ADB . Atlantic Development Board (Canada). 



ADF BEARING INDICATOR . An instrument used with a 

 radio direction finder to indicate automatically 

 the relative, magnetic, or true bearing (or recip- 

 rocal) of a transmitter. A manual type of such an 

 instrument is called an MDF bearing indicator. (17) 



ADG . U. S. Navy ship designation for a Degaussing 

 Vessel. 



ADIABATIC . Without gain or loss of heat. (17) 



ADIABATIC PROCESS . A thermodynamic change of state 

 of a system in which there is no transfer of heat 

 or mass across the boundaries of the system. In an 

 adiabatic process, compression always results in 

 warming, expansion in cooling. In meteorology the 

 adiabatic process is often also taken to be a 

 reversible process. (24) 



ADIABATIC TEMPERATURE GRADIENT . The adiabatic 

 temperature change on a vertical distance of 1000 

 meters. (13) 



ADVANCE (OF A BEACH) . 1. A continuing seaward 

 movement of the shore line. 



2. A net seaward movement of the shoreline 



over a specified time. Also called progression. 



(11) 



ADVECTION FOG . A type of fog caused by the advec- 

 tion of moist air over a cold surface, and the con- 

 sequent cooling of that air to below its dew point. 

 A very common advection fog is that caused by 

 moist air in transport over a cold body of water 

 (SEA FOG) . (24) 



AE . U. S. Navy designation for an Ammunition Ship. 



AEC. Atomic Energy Commission. 



AEROEMBOLISM . 1. The formation or liberation of 

 gases in the blood vessels of the body, as brought 

 on by a change from a high, or relatively high, 

 atmospheric pressure to a lower one. 2. The 

 disease or condition caused by the formation or 

 liberation of gases in the body. The disease is 

 characterized principally by neuralgic pains, 

 cramps, and swelling, and sometimes results in 

 death. Also called 'decompression sickness'. (31) 



Aeroembolism can occur to scuba swimmers and 

 divers on ascent from even shallow depths. How- 

 ever, it can almost always be prevented by main- 

 taining relaxed respiration upon ascent and avoiding 

 breath holding. Because the disorder forces air 

 bubbles into the blood stream it may be serious, 

 resulting in convulsions, pain, paralysis, reflex 

 spasms or even death. Treatment involves immediate 

 recompression in a pressure chamber. (37) 



AEROLOGY . 1. As officially used in the U. S. Navy 

 until early 1957, same as METEOROLOGY; however, 

 this usage tended to be more administrative than 

 scientific. 2. As a subdivision of meteorology, 

 the study of the free atmosphere throughout its 

 vertical extent, as distinguished from studies con- 

 fined to the layer of the atmosphere adjacent to 

 the earth's surface. (24) 



AES . Atlantic Estuarine Society. 



AESTIVAL . Of or pertaining to summer. The corres- 

 ponding term relating to winter is hibernal. (17) 



AF. U. S. Navy designation for a Store Ship. 



AFAC. American Fisheries Advisory Committee. 



"A" FRAME . Gallows used for leading wires over 

 the side of a ship. (38) 



AFS . U. S. Navy designation for a Combat Store 

 ship. 



AFS . American Fisheries Society. 



AG . U. S. Navy ship designation for Miscellaneous 

 Auxiliary. 



AGAR. A dried and bleached gelatenous extract 

 obtained from several kinds of red algae. It is 

 used extensively in medicine, chiefly as a laxative, 

 since it is not digested and increases greatly in 

 bulk with the absorption of water. Also used as 

 an essential ingredient in the preparation of a 

 medium for the growth of bacteria and fungi. (18) 



AGB. 



U. S. Navy ship designation for an Icebreaker. 



AGC . U. S. Navy designation for an Amphibious 

 Force Flagship, Also AGC is used to mean Automatic 

 Gain Control. 



AGDE. U. S. Navy designation for an Escort 

 Research Ship. 



AGE. WAVE . The ratio of wave velocity to wind 

 velocity (in wave forecasting theory). (10) 



AGEH . U. S. Navy designation for a Hydrofoil 

 Research Ship. 



AGGER . See DOUBLE TIDE. 



AGGRADATION . The geologic process by means of 

 which various parts of the surface of the earth 

 are raised in elevation or built up by the deposi- 

 tion of material eroded from other sections and 

 transported thereto by water or wind. See 

 ACCRETION. (27) 



AGGREGATE . A mixture of substances, separable by 

 mechanical means . 



