PARALLAX INEQUALITY 



In reading several diflFerent types of oceano- 

 grapliic instruments, errors of parallax are 

 easily introduced if the line of sight is not care- 

 fully maintained perpendicular to the reading 

 scale. Parallax errors are of particular concern 

 in reading liquid-in-glass thermometers. 



parallax inequality — The variation in the range 

 of tide or in the speed of tidal currents because 

 of the continual change in the distance of the 

 moon from the earth. The range of tide and 

 speed of tidal currents tend to increase as the 

 moon approached perigee and to decrease as it 

 approached apogee. (50) 



parallel — See parallel of latitude (sense 1). 



parallel of latitude — 1. (also called parallel) . A 

 circle (or approximation of a circle) on the sur- 

 face of the earth, parallel to the Equator, and 

 connecting points of equal latitude. 



2. (also called circle of longitude) . A circle 

 of the celestial sphere, parallel to the ecliptic, 

 and connecting points of equal celestial latitude. 

 (68) 



paralytic shellfish poisoning — An intoxication in 

 humans resulting from the ingestion of marine 

 mollusks, usually mussels or soft clams, that 

 become toxic during periods of higli concentra- 

 tions of certain dinofiagellates. The effects 

 range from mild discomfort to fatal respiratory 

 paralysis, with symptoms including tingling or 

 burning of the lips, gums, tongue, and face fol- 

 lowed l3y numbness of the extremities, a general 

 feeling of weakness and dizziness, inability to 

 coordinate muscular movements, and respira- 

 tory distress. 



parameter — 1. In general, any quantity of a 

 problem that is not an independent variable. 

 More specifically, the tenn is often used to dis- 

 tinguish, from dependent variables, quantities 

 which may be more or less arbitrarily assigned 

 values for purposes of the problem at hand. 



{Note: Carelessly used by many oceanogra- 

 phers for almost any oceanographic quantity or 

 element.) 



2. In statistical terminology, any numerical 

 constant derived from a population or a prob- 

 ability distribution. Specifically, it is an arbi- 

 trary constant in tlie mathematical expression 

 of a probability distribution. 

 (5) 



parapodium — K paired lateral locomotive struc- 

 ture on body segments of polychaetes. 



parasitic nutrition— That process by which an 

 organism absorbs organic food directly from 

 the body of its host. See hetereotrophic nutri- 

 tion. 



parasitism — A relationship between two species 

 in which one lives on or in the body of its host, 

 and obtains food from its tissues. Some au- 

 thorities distinguish between a "commensal 

 parasite,'' which obtains nourishment from its 

 host without causing harm, and a "pathogenic 



parasite," which benefits at the expense of its 

 host. 



parent — A radionuclide that upon distintegra- 

 tion yields a specified nuclide, either directly or 

 as a later member of a radioactive series. (70) 



partial node — The point, line, or surface, in a 

 standing wave system where some characteristic 

 of the wave field has a minimum amplitude dif- 

 fering from zero. (6) 



partial tide — (also called tidal component, tidal 

 constitutent) . One of the harmonic components 

 comprising the tide at any point. The periods 

 of the partial tides are derived from various 

 combinations of the angular velocities of earth, 

 sun, moon, and stars relative to each other. See 

 constituent. (5) 



THE BASIC COMPONENTS OF THE TIDE-PRODUCING FORCES 



[AFn« SVEtORUP. ET. AL.. 1949) 



particles — See grains. 



particle velocity — In ocean wave studies, the in- 

 stantaneous velocity of a water particle under- 



going orbital motion. 



At the crest, its direc- 



tion IS the same as the direction of progress of 

 the wave, and at the trough it is in the opposite 

 direction. (5) 



parts per thousand — See per mille. 



Pascal's law — Pressure exerted at any point upon 

 a confined liquid is transmitted undiminished in 

 all directions. 



pass — A narrow connecting channel between two 

 bodies of Avater; also the inlet tlirough a bar- 

 rier reef atoll or sand bar or a navigable chan- 

 nel at a river's mouth. (2) 



passage — A narrow navigable pass or channel 

 between two laiidmasses or shoals. (68) 



passive sonar — A method or equipment by which 

 information concerning a distant object under- 

 water is obtained by evaluating the sound gen- 

 erated by the object itself. (3) 



patch — 1. A collection of pack ice, less than 10 

 kilometers (5.4 nautical miles) across. (74) 



2. An irregular cluster of floating sea ice frag- 

 ments of any concentration. (59) 



120 



