the range over which it will produce a useable 

 acoustic signal in the water as a transmitter, 

 or a useable electrical signal as a listening 

 device. Instruments are generally operable over 

 a range that is considerably wider than the range 

 in which they may be calibrated or may be recipro- 

 cal. They are not necessarily stable over the 

 entire operating range. In addition, directivity 

 patterns may be poor and frequency response rough 

 beyond the reciprocity range. (1) 



OPERCULUM . The plate covering the gills of a bony 

 fish; also, the plate serving to cover the opening 

 of some snail shells. (19) 



OPPOSING WIND . In wave forecasting, a wind blow- 

 ing in the opposite direction to that in which the 

 waves are travelling. (11) 



OPTICAL PROCESSING . Light, including visible and 

 infrared, has a relatively high frequency, which 

 means that larger bandwidths and higher rates 

 are potentially available for handling data pro- 

 cessing information. Performing logical func- 

 tions with electronic devices requires the moving 

 of electrons, and here one must deal with, and is 

 limited by, the inductance and capacitance of 

 transmission lines and devices. By using light 

 and treating it as a wave (interference effects) 

 or as a particle quantum interaction) new classes 

 of circuits appear possible which are not charge 

 limited. Considerably higher "fan outs" in the 

 order of 100 to 1000 have been achieved in op- 

 tical systems at millisecond speeds. 



ORANGE PEEL BUCKET SAMPLER . This sampler is used 

 primarily to obtain bottom samples in shallow water 

 and several sizes are available. The size con- 

 sidered here weighs 45 pounds and holds about 300 

 cubic inches of sediment. A small hook, attached to 

 the end of the lowering wire, supports the sampler 

 as it is lowered and also holds the jaws (four 

 curved triangular blades which form a hemisphere 

 when closed) in the open position. When contact 

 with the bottom is made the sampler jaws sink into 

 the sediment and the wire tension is released, al- 

 lowing the hook to swing free of the sampler. Upon 

 hoisting, the wire takes a strain on the closing 

 line which is also attached to a handle which ac- 

 tivates a ratchet chain and sheave that close the 

 jaws. The closing line supports the sampler as it 

 is being hoisted. To prevent washing out of the 

 sample from the top, a canvas cover is frequently 

 used. (35) 



ORBIT . In water waves, the path of a water par- 

 ticle affected by the wave motion. In deep water 

 waves the orbit is nearly circular and in shallow 

 water waves the orbit is nearly elliptical. In 

 general, the orbits are slightly open in the direc- 

 tion of wave motion giving rise to MASS TRANSPORT. 

 (11) 



ORBITAL CURRENT . The flow of water accompanying 

 the orbital movement of the water particles in a 

 wave. Not to be confused with wave-generated 

 LITTORAL CURRENTS. (11) 



ORBITAL MOTION . In hydrodynamics, the motion of 

 a fluid particle induced by the passage of a pro- 

 gressive GRAVITY WAVE. When the wave height is 

 small and the fluid depth is great, the orbit is 

 a circle whose radius decreases exponentially with 

 depth. In shallow fluid the orbit is an ellipse, 

 which degenerates into a horizontal line at the 

 bottom boundary of the fluid. (12) 



ORDA . Oceanographic Research for Defense Applica- 

 tion. 



ORDER OF MAGNITUDE (A FACTOR OF 10) . Two quanti- 

 ties of the same kind which differ by less than a 

 factor of 10 are said to be of the same order of 

 magnitude. 'Order of magnitude' is used loosely 



by many writers to mean a pronounced difference in 

 quantity but with the difference much less or much 

 more than a factor of 10. (31) 



ORDINARY TIDES . 1. This expression is not used 

 in a technical sense by the Coast and Geodetic 

 Survey, but the vrord "ordinary" when applied to 

 tides , may be taken as the equivalent of the word 

 "mean". Thus, "ordinary high water line" may be 

 assumed to be the S£une as '\nean high water line." 



2. Waves having periods of 12 

 hours to 24 hours . (14) 



OROGENY. An EPOCH of mountain building, usually 

 associated with the formation of a fold mountain 

 range; for example, the Caledonian orogeny which 

 built mountains in north-west Britain and Scandi- 

 navia from a geosynclinal environment, during the 

 Palaeozoic era. (27) 



OROGRAPHY . A branch of physical geography which 

 treats with mountains . 



ORSA . Operations Research Society of America. 



ORSTOM. Office de la Recherche Scientifique et 

 Technique d 'outre Mer. 



ORTHOGONAL . On a refraction diagram, a line drawn 

 perpendicular to the wave crests. (11) 



OS. OCEAN STATION. 



OSCILLATION . Oscillation is the variation, usually 

 with time, of the magnitude of a quantity with 

 respect to a specified reference when the magnitude 

 is alternately greater and smaller than the refer- 

 ence. (2) 



OSCILLATORY WAVE . A wave -in which each individual 

 particle oscillates about a point with little or 

 no permanent change in position. The term is com- 

 monly applied to progressive oscillatory waves in 

 which only the form advances, the individual par- 

 ticles moving in closed orbits. Distinguished from 

 a WAVE OF TRANSLATION. (11) 



OSCILLOSCOPE . An instrument for showing visually 

 graphical representations of the waveforms encoun- 

 tered in electrical circuits. (36) 



OST . Office of Science and Technology. 



OSV . Ocean Station Vessel. 



OSW. Office of Saline Water (Department of 

 Interior) . 



OTITIS EXTERNA . An infection of the external ear 

 canal. A frequent physical disorder incurred in 

 SCUBA diving. (37) 



OUTFALL . 1. The vent of a river, drain, etc. 



2. A structure extending into a body of 

 water for the purpose of discharging sewage, storm 

 runoff, or cooling water. (11) 



OUTPUT CURRENT . The output current of a transducer 

 connected to a given source is the rms current 

 which would be measured at its load terminals if 

 they were short-circuited. (4) 



OUTPUT IMPEDANCE . The output impedance of a trans- 

 ducer connected to a given source is the impedance 

 which would be measured at its load terminals if 

 they were not connected to a load and if the source 

 voltage of the source were zero. (4) 



OUTPUT POWER . The output power of a transducer 

 connected to a given source is the available power 

 at its load terminals . (4) 



OUTPUT VOLTAGE . The output voltage of a transducer 



86 



