PLUNGE POINT . 1. For a plunging wave, the point 

 at which the wave curls over and falls. 



2. The final breaking point of the 

 waves just before they rush up on the beach. (11) 



PLUTONIC ROCK . Igneous rocks which have cooled 

 some distance below the surface and usually possess 

 phaneritic (coarse-grained) structures. (27) 



PMR. 



Pacific Missile Range (BuWeps). 



PNEUMOTHORAX . If the surface of the lung is 

 accidentally ruptured by a sudden excessive pres- 

 sure inside the lungs, or if the chest wall is 

 perforated by some external means, air will be 

 pulled in between the membranes when the chest 

 expands. An actual air pocket will then exist 

 between the lung and the chest wall. This con- 

 dition is known as pneumothorax (pneumo-air/ 

 thorax-chest) and may occur as an accident in 

 diving or submarine escape. (37) 



PNL. Pacific Naval Laboratory. 



PDF I . Pacific Oceanographic Fisheries Investiga- 

 tion. 



POG. Pacific Oceanographic Group (British 

 Columbia) . 



POIKILOTHERMOUS . Cold-blooded animals whose body 

 temperatures are essentially at those of the en- 

 vironment in which they live. (19) 



POINT . The extreme end of a cape; or the outer end 

 of any land area protruding into the water, usually 

 less prominent than a CAPE. (11) 



POISSON'S RATIO . The ratio of lateral strain to 

 corresponding axial strain for a material sub- 

 jected to axial loading. Poissons ratio for an 

 isotropic material at a stress below the PROPOR- 

 TIONAL LIMIT may be calculated: E 



2G 



where : 



r ■= Poissons Ratio 



E = Modulus of Elasticity in Tension or Com- 

 pression 

 G = Modulus of Elasticity in Shear, psi. 



POLAR ICE . Polar ice is the thickest and heaviest 

 form of SEA ICE more than one year old. Undis- 

 turbed polar ice is about 12 feet thick on the 

 average. (25) 



POLDER . Land reclaimed from the sea or other body 

 of water by the construction of an embankment to 

 restrain the water, (17) 



POLYAXON . See SPICULE. 



POLYMORPHISM . The existence of individuals of more 

 than one form in a species. (19) 



POLYNYA (ICE CLEARING) . A frequently used Russian 

 term for a water area, other than a lead, lane or 

 crack, which is surrounded by sea ice. The term 

 window is sometimes used for a similar open area 

 in river ice. (24) 



POLYZOA . Broyozoa, a colonial animal that secretes 

 a calcareous, horny, or membraneous covering in a 

 multitudinous variety of forms and structures. 

 Bryozoa may form insignificant colonies on shells, 

 or they may be an important constituent of a reef. 

 (16) 



POROROCA. See BORE. 



POROSITY. The percentage of pore space in the 

 total volume of the dry bottom sediment sample. 

 This percentage expresses the volume that can be 

 occupied by water. (27) 



PORT. 1. A place provided with terminal and trans- 

 fer facilities for loading and discharging cargo or 

 passengers, usually located in a harbor. 



2. The left side of a craft, facing for- 

 ward. The opposite is STARBOARD. (17) 



PORTABLE PNEUMATIC CORE SAMPLER . This device, 

 which weighs 700 pounds, was developed by the U. S. 

 Navy Ordnance Laboratory for sampling coral and 

 sand bottoms. It consists of a 4-legged pyramidal 

 frame about 8 feet high, a pneumatic hammer with 

 air supply and exhaust hosing, 400 pounds of lead 

 weight, an anvil, and a 4-foot long aluminvmi barrel 

 with a driving head for cutting through coral. (35) 



PORTABLE TIDE STAFF . See TIDE STAFF. 



PORTUGUESE MAN OF WAR . This familiar stinging 

 jelly fish is strictly speaking not a true jelly 

 fish but a hydroid found floating on the surface 

 of the sea. The Portuguese Man of War (Physolia) 

 has a world wide distribution in temperate and 

 tropical waters. Venom cells and stinging appara- 

 tus are contained in its long trailing tenacles 

 which are suspended from a balloon-like float. Its 

 sting causes a urticarial lesion on the skin of its 

 human victim. 



POSITION BUOY . An object towed astern to assist a 

 following vessel in maintaining the desired or 

 prescribed distance, particularly in conditions of 

 low visibility. Also called fog buoy, towing spar. 

 (17) 



POSITIVE GRADIENT . Describes conditions in layers 

 where the temperature increases with increasing 

 depth. (3) 



POTENTIAL ENERGY (OF WAVES ) . In a progressive os- 

 cillatory wave, the energy resulting from the ele- 

 vation or depression of the water surface from the 

 undisturbed level. This energy advances with the 

 wave form. (11) 



POTENTIOMETER . A variable voltage divider. (36) 



POTENTIOSTAT . A device used for the direct study 

 of corroding metals where both anodic and cathodic 

 reactions are taking place simultaneously. 



POWER GAIN . Power gain in decibels is the amount 

 by which the output power level in decibels exceeds 

 the input power level in decibels. Thus, if the 

 output power of a device is ten times that of the 

 input, the power gain is ten decibels. On the 

 other hand, if the output is one hundred times that 

 of the input, the gain is twenty decibels. (9) 



POWER LEVEL . Power level, in decibels, is ten times 

 the logarithm to the base ten of the ratio of a 

 given power to a reference power. The reference 

 power must be indicated. (2) 



POWER PER UNIT BAND . The limit approached by the 

 quotient obtained by dividing (1) the power of the 

 energy being transmitted by a given system, at a 

 given time and in a given frequency band, by (2) 

 the width of this band as the width of this band 

 approached zero. (4) 



POWER SPECTRUM . See SPECTRUM DENSITY. 



PPI. Plan Position Indicator. A scope (i.e., 

 radarscope) on which reflections are so depicted 

 to indicate the range and bearing of objects. 



PRECISION DEPTH RECORDER (PDR) . This recorder 

 uses an electro-sensitive paper, has a paper speed 

 of 24 inches per hour, and displays 400 fathoms 

 over a width of 18.85 inches. It phases automati- 

 cally so that depths to the full range capability 

 of the sonar set can be recorded in increments of 

 400 fathoms with high precision. The PDR triggers 



92 



