ing the directional characteristics of the trans- 

 ducer. It is usually an axis of structural sym- 

 metry, or the direction of maximum response; but 

 if these do not coincide the reference direction 

 must be described explicitly. (1) 



PROGRESSION (OF A BEACH) ■ See ADVANCE. 



PROGRESSIVE WAVE . A wave whose crest advances 

 horizontally. For a wave with a length less than 

 the depth of the water, the rate of advance depends 

 upon the wave length and may be expressed by the 

 formula: r = (gL/2TT )^ = 2.26 \/L, in which r is 

 the rate of advance in feet per second, g is equal 

 to 32.17, L the length of wave in feet, and t is 

 equal to 3.1416. The corresponding wave period (P) 

 may be expressed by the formula: P (in seconds) 

 = (2tt L/g)% 0.442 /TT. For a progressive tidal 

 wave with a length many times as great as the depth 

 of water, the rate of advance is independent of the 

 wave length but is determined by the depth of the 

 water and may be expressed by the formula: r 



y/gd = 5.67 t/d', in which d is the depth of water in 

 feet, the other symbols being the same as previous- 

 ly given. The corresponding per iod may be expres- 

 sed by the formula: P = L/ i/gd" = 0.176L//dT (14) 



PROJECT NEPTUNE . An Office of Naval Research (ONR) 

 program designed to demonstrate the feasibility of 

 using EXPENDABLE (Marine) INSTRUMENTATION on ships 

 of the Merchant fleet. 



PROJECTOR . An underwater acoustic transmitter. 

 See UNDERWATER SOUND PROJECTOR, SPLIT PROJECTOR. 

 (6) 



PROJECTOR LOSS . The projector loss of a sonar 

 transducer, used for the transmission of acoustic 

 energy, at a specified frequency, may be defined 

 as the transmission loss measured by the ratio of 

 (1) the input power of the electric energy delivered 

 to the transducer to (2) the resulting load power 

 of the acoustic energy delivered by the transducer 

 to a water surface having an area of one square 

 centimeter and lying perpendicular to the maximum 

 response reference axis of the transducer at its 

 index point. (4) 



PROLATE CYCLOID . See TROCHOID. 



PROMONTORY . A high point of land projecting into 

 a body of water; a HEADLAND. (11) 



PROPAGATION ANOMALY . The difference between the 

 actual propagation loss for a given length of 

 water path and the nominal value of propagation 

 loss identified with the distance covered by that 

 path is known as the propagation anomaly. (4) 



PROPAGATION LOSS . Propagation loss may be defined 

 as the transmission loss association with any given 

 length of ray path in the water. (4) 



PROPAGATION VELOCITY . (See WAVE VELOCITY) . 



PROPORTIONAL BAND LEVEL CHARACTERISTIC . A propor- 

 tional band level characteristic is one in which 

 the band levels of a series of proportional bands 

 are plotted against their geometric mean frequen- 

 cies, or against their upper or lower boundary 

 frequencies. (4) 



PROPORTIONAL BANDS . Whenever the members of a 

 series of frequency bands have equal band ratios 

 the bands are said to be proportional bands. (4) 



PROPORTIONAL LIMIT . The proportional limit repre- 

 sents an aspect of elastic behavior similar to the 

 elastic limit, the principal difference lying in 

 the method of determination. The straight-line 

 proportionality between stress and strain in the 

 elastic range has already been discussed. It is 

 the upper limit of the range of proportionality 



that defines the proportional limit. In other 

 words, the proportional limit is the greatest 

 stress which a material is capable of developing 

 without a deviation from the law of proportionality 

 (Hooke's Law). 



In practice, the proportional limit is deter- 

 mined from a plot of stress against strain, being 

 taken as the stress at the first visible departure 



— Proportional 

 Limit 



Strain 



from the straight line drawn through the points in 

 the elastic range. Since the departure from 

 linearity is in general quite gradual, the deter- 

 mined value will depend on the accuracy and sen- 

 sitivity of the strain-measuring device employed in 

 the test. The experimentally determined value for 

 a given material will be found to decrease as the 

 sensitivity of extensometer used is increased, 

 that is, as the ability to detect smaller and smal- 

 ler strain increments is increased. Because of 

 these uncertainties, proportional limit is very 

 seldom employed in specifications. 



PROTON . The positive particles of an atom. The 

 smallest quantity of positive electricity which 

 can exist in a free state; associated with elec- 

 trons and neutrons, it makes up the atom. (36) 



PROTOPLASM . Living substance; the complex colloi- 

 dal physico-chemical system that constitutes liv- 

 ing matter and is the viscid, semifluid material of 

 animal and plant cells. (19) 



PROTOTYPE . In laboratory usage, the original 

 structure, concept, or phenomenon used as a basis 

 for constructing a scale model or copy. (11) 



PROTOZOANS . Minute one-celled animals, most of 

 which are invisible to the naked eye and occur 

 universally in the surface layers of the sea. 

 Several genera are capable of producing biolumines- 

 cence, usually of the sheet type. (15) 



PROVINCE . A region composed of a group of similar 

 bathymetric features whose characteristics are 

 markedly in contrast with surrounding areas. (26) 



PSA. Pacific Science Association. 



Founded 1920 in Honolulu. 



Activities: PSA is a private international 

 association of scientists interested in problems 

 of the Pacific Ocean. The Association sponsors a 

 Pacific Science Congress every three years. The 

 main objectives are the promotion of scientific 

 study of problems of the Pacific region, exchange 

 of information, and the publication of reports of 

 congresses and a Pacific Science Bulletin. 



PSAC . President's Scientific Advisory Committee. 



PSEUDOCHITIN . See TECTIN. 



PS EUDO PODIUM . A flowing extension of protoplasm 



used in locomotion or feeding by a cell or proto- 

 zoan. (19) 



PSMFC. Pacific States Marine Fisheries Commission. 



PSMSL. Permanent Service for Mean Sea Level. 



91* 



