NATURAL SLOPE . See ANGLE OF REPOSE. 



NAUTICAL . Of or pertaining to ships , navigation 

 (chiefly marine), or seamen. In contrast, naviga- 

 tional refers to navigation only, marine refers to 

 the sea, maritime indicates relationship or proxi- 

 mity to the sea, and naval refers to the Navy. (17) 



NAUTICAL MILE . The distance unit in the nautical 

 system, defined as the length of one minute of arc 

 along any great circle on the earth's surface. 

 Since this actual distance varies slightly with 

 latitude, a nautical mile by international agree- 

 ment is defined as 1852 meters (6076.103 feet or 

 1.1508 statute miles). (24) 



NAVAL ENGINEERING . According to the American 

 Society of Naval Engineers, Naval Engineering is 

 the art and science applied in the design, construc- 

 tion, operation and maintenance of naval ships and 

 their installed equipment. 



NAVAIRLANT . Naval Air Forces, Atlantic. 



NAVAIRPAC . Naval Air Forces, Pacific. 



NAVFORJAP . Naval Forces, Japan. 



NAVFORKOR . Naval Forces, Korea. 



NAVIER-STOKES EQUATIONS . The equations of motion 

 for a viscous fluid which may be written 



dl= _ 1 ^+ F+ vV^V+ivV(V-V), 

 at p 3 



where p is the pressure, p the density, F the 

 total external force, v the fluid velocity, and 



V the kinematic viscosity. For an incompres- 

 sible fluid, the term in V ' V (divergence) 

 vanishes and the effects of viscosity then play a 

 role analogous to that of temperature in thermal 

 conduction and to that of density in simple dif- 

 fusion. 



Solutions of the Navier-Stokes equations have 

 been obtained only in a limited number of special 

 cases; in atmospheric motion, the effects of 

 molecular viscosity are usually overshadowed by 

 the action of turbulent processes and the Navier- 

 Stokes equations have been of little direct ap- 

 plication. The use of the concept of eddy viscosity 

 has overcome this limitation in certain problems . 



The equations are derived on the basis of 

 certain simplifying assumptions concerning the 

 stress tensor of the fluid; in one dimension they 

 represent the assumption referred to as the 

 Newtonian friction law. (24) 



NAVMAR . Naval Forces, Marianas. 



NAVOCEANO . U. S. Naval Oceanographic Office. 



NAVOCS . Naval Officer Candidate School (USN) . 

 NAVPHIL. Naval Forces, Philippines. 

 NAVSAT . Navigational Satellite. 



NAVSUPORANT . Naval Support Forces, Antarctica. 



NAVUWSEC . U. S. Naval Underwater Weapons Systems 

 Engineering Center, Newport, Rhode Island. 



NBS . National Bureau of Standards. 



NCEL. Naval Civil Engineering Laboratory, U. S. 

 Navy (BuDocks) Port Hueneme, California. 



NCOR. National Committee on Oceanographic Re- 

 search. 



NEAP RISE . The height of neap high water above 

 the plane of reference or datum of chart. (14) 



NEAP TIDES OR TIDAL CURRENTS. 



Tides of de- 



creased range or tidal currents of decreased 

 velocity occurring semi-monthly as the result of 

 the moon being in quadrature. The neap range of 

 tide is the average semidiurnal range occurring 

 at the time of neap tides and is most conveniently 

 computed from the harmonic constants. It is smal- 

 ler than the mean range where the type of tide is 

 either semidiurnal or mixed and is of no practical 

 significance where the type of tide is diurnal. 

 The average height of the high waters of the neap 

 tide is called neap high water or high water neaps 

 and the average height of the corresponding low 

 waters is called neap low water or low water neaps . 

 (14) 



2. The tides occur- 

 ring near the times of first and last quarter of 

 the moon, when the range of tide tends to decrease. 

 Tides occurring near the times of full and new moon 

 when the range tends to increase are called SPRING 

 TIDES. (17) 



NEARSHORE CIRCULATION . The ocean circulation pat- 

 tern composed of the NEARSHORE CURRENTS and COAST- 

 AL CURRENTS. (11) 



NEARSHORE (ZONE) . In beach terminology an indef- 

 inite zone extending seaward from the shore line 

 somewhat beyond the breaker zone. It defines the 

 area of NEARSHORE CURRENTS. The SHOREFACE. (11) 



NECK . The narrow band of water flowing seaward 

 through the surf. (11) 



NEENAH PAPER EXPANS IMETER . A device used to 

 evaluate the dimensional stability of paper 

 material for the construction of maps. 



NEES . Naval Engineering Experimental Station, 

 Annapolis , Maryland . 



NEGATIVE GRADIENT . Describes conditions in a layer 

 where the temperature decreases with increasing 

 depth. (3) 



NEKTON . A division made up of all the swimming 

 animals found in the pelagic division. (See MARINE 

 LIFE) 



NEL. Navy Electronics Laboratory, U. S. Navy, 

 San Diego, California. 



NEL DREDGE . Designed by the U. S. Navy Electron- 

 ics Laboratory, this dredge is constructed of a 1/4 

 inch steel plate, and is 1 foot deep, 2 feet wide, 

 and 3 feet long. The forward end is open, but the 

 aft end has a heavy grill of 3/4 inch round steel 

 bars. This grill is designed to retain large rock 

 samples. When it is desired to obtain finer sized 

 material, a screen of heavy hardware cloth is 

 placed over the grill. A bridle consisting of 7- 

 foot lengths of galvanized steel chain on 1/2 inch 

 wire is attached to shackling tabs on the sides of 

 the dredge. The bridle is attached to a swivel 

 which is made fast to a 1/2 inch diameter lowering 

 wire. During dredging operations, the ship is hove 

 to as the dredge is lowered. A boom or boat crane, 

 1/2 inch wire, and dynamometer to indicate bottom 

 contact are used. Towing the dredge along the bot- 

 tom should be done only by ships that can operate 

 at very slow speeds; i.e., at 2 or 3 knots. (35) 



NEPHELOMETER . An instrument which measures the 

 scattering of light by determining the amount of 

 light emitted at right angles to the original beam 

 direction. 



Such devices are useful in studies of particles 

 (size and amount) suspended in water. (35) 



NEAP RANGE. See NEAP TIDES. 



NERITIC . Shallow water marine environment. (27) 



81 



