LANG LAY . See WIRE ROPE. 



LARV I PAROUS . See OVIPAROUS, 



LASER . Light Amplification by Stimulated Emission 

 of Radiation. 



LATENT HEAT . Heat resulting in a change in state 

 but no temperature change. (33) 



LATITUDE . The latitude of any point is the angle 

 between the local plumb line and the equatorial 

 plane. Because the earth can be considered as hav- 

 ing the form of a spheroid, and as the plumb line, 

 for all practical purposes, is perpendicular to the 

 surface of the spheroid, any plane parallel to the 

 Equator cuts the surface of the spheroid in a cir- 

 cle, and all points on this circle have the same 

 latitude. These circles are called PARALLELS OF 

 LATITUDE. Latitude is measured in degrees, minutes, 

 and seconds north and south of the Equator. Since 

 the earth is not a sphere the distance represented 

 by a unit of latitude increases by about 1 per cent 

 between the Equator and the Poles. At the Equator, 

 1 degree of latitude is equivalent to 110,567.2 

 meters, and at the Poles it is 111,699.3 meters. 

 (13) 



LAYER DEPTH . In oceanography, the thickness of 

 the MIXED LAYER; or the depth to the top of the 

 THERMOCLINE. (12) 



LAYER EFFECT . Reduction in the echo and listening 

 ranges on a target located within or beneath a 

 thermocline. 



LAYER OF NO MOTION . A layer, assumed to be at 

 rest, at some depth in the ocean. This implies 

 that the isobaric surfaces within the layer are 

 level, and hence they may be used as reference 

 surfaces for the computation of absolute gradient 

 currents . 



This same concept can define a level of no 

 motion or a surface of no motion. (12) 



LCU. U. S. Navy designatio i for a Utility Landing 

 Craft. 



LEAD . A long narrow but navigable water passage 

 in PACK ICE. A lead may be covered by thin ice. 

 (25) 



LEAD LINE . See SOUNDING LINE. 



LEAGUE . A unit of distance of indefinite value, 

 varying from 2.4 to 4.6 miles. In the U.S. it is 

 approximately 3 miles, either statute or nautical. 

 (17) 



LEDGE . A rocky formation continuous with and fring- 

 ing the shore. (27) 



LEE . (1) Shelter, or the part or side sheltered or 

 turned away from the wind or waves. (2) (Chiefly 

 nautical) The quarter or region toward which the 

 wind blows . (11) 



LEEWARD . The direction toward which the wind is 

 blowing; the direction toward which the waves are 

 travelling. (11) 



LEEWARD TIDE . A tidal current setting in the same 

 direction the wind is blowing. A tidal current 

 setting in the opposite direction is called a wind- 

 ward tide. Also called lee tide. (17) 



LEFT LAY . See WIRE ROPE. 



LENGTH OF WAVE . The horizontal distance between 

 similar points on two successive waves measured 

 perpendicularly to the crest. (11) 



LEVEE . An embankment bordering one or both sides 

 of a CANYON or SEACHANNEL. (27) 



LEVEL . In acoustics, the level of a quantity is 

 the logarithm of the ratio of that quantity to a 

 reference quantity of the same kind. The base of 

 the logarithm, the reference quantity, and kind of 

 level must be specified. (2) 



LEVEL SURFACE . An imaginary surface along which 

 no component of gravity acts. 



LGO . Lamont Geological Observatory. 



LIGHTED BUOY . A buoy with a light having definite 

 characteristics for detection and identification 

 during darkness. If the light is produced by gas, 

 it may be called a gas buoy. (17) 



LIGHTED SOUND BUOY . A lighted buoy provided with 



a sound signal, 

 buoy. (17) 



This is one type of combination 



LILY -PAD ICE . Pancake ice when the cakes are not 

 more than about 18 inches in diameter. (17) 



LIMESTONE . A sedimentary rock consisting essen- 

 tially of the mineral calcite (calcium carbonate). 

 (27) 



LIMITING RAY . Any ray which is tangent to a plane 

 at which the velocity of propagation has a maximum 

 value, either at a boundary of the medium or at a 

 level where the velocity gradient changes sign, is 

 known as a limiting ray. (4) 



LIMIT OF BACKRUSH . See BACKRUSH. 



LINEAR TRANSDUCER . A linear transducer is a trans- 

 ducer for which the pertinent measure of all the 

 waves concerned are linearly related. (1) 



LINE HYDROPHONE . A line hydrophone is a directional 

 hydrophone consisting of a single, straight-line 

 element, or any array of contiguous or spaced elec- 

 troacoustic transducing elements, disposed on a 

 straight line, or the acoustic equivalent of such 

 an array. (1) 



LINE OF CENTERS . When considering the paths of 

 rays in a vertical plane crossing a region of con- 

 stant vertical velocity gradient the intersection 

 of the vertical plane with the horizontal level of 

 zero velocity is known as the line of centers. (4) 



LINE SPECTRUM . 1. If the frequencies of the 

 sinusoidal components making up a complex wave 

 are separated by intervals on the frequency scale 

 of such magnitude that the magnitude of each 

 component may be independently evaluated, the wave 

 is said to have a line spectrum. (4) 



2. A line spectrum is a spectrum 

 whose components occur at a number of discrete 

 frequencies. (1) 



LINE SQUALL . See SQUALL. 



LIPPER . 1. Slight ruffling or roughness on a 

 water surface. 



2. Light spray from small waves. (17) 



LISTENING SONAR. See PASSIVE SONAR 



LITHOLOGY . (1) Study of the characteristics of 

 rocks . 



(2) Study of the composition of rocks, 

 (27) 



LITHOPHYTE . A plant or plantlike organism that 

 grows on the surface of rocks. (20) 



LESSER FLOOD. See FLOOD CURRENT. 



LITHOSPHERE. The solid crust of the earth. (27) 



68 



