agalnsc interference restricted to a known narrow 

 frequency band are described as reverberation- 

 suppression filters. (4) 



REVERSE BLOCKED ADMITTAMCE . The reverse blocked 

 admittance of a transducer is the reciprocal of 

 the reverse free impedance. (4) 



REVERSE BLOCKED IMPEDANCE . The reverse blocked 

 impedance of a transducer is its output impedance 

 when its source terminals are open-circuited. (4) 



REVERSE FREE ADMITTANCE . The reverse free admit- 

 tance of a transducer is the reciprocal of its 

 reverse blocked impedance. (4) 



REVERSE FREE IMPEDANCE . The reverse free impedance 

 of a transducer is its output impedance when its 

 source terminals are short-circuited. (4) 



REVERSE LAY . See WIRE ROPE. 



REVERSIBLE TRANSDUCER . Also Bilateral transducer. 

 A transducer which, when connecting any energy 

 source and an energy load, completes a system which 

 satisfies the principle of reciprocity is known as 

 a reversible transducer. (4) 



REVERSING CURRENT . A tidal current that flows al- 

 ternately in approximately opposite directions with 

 a slack water at each reversal of direction. Cur- 

 rents of this type usually occur in rivers and 

 straits where the direction of flow is more or less 

 restricted to certain channels. When the movement 

 is towards the shore or up a stream, the current is 

 said to be flooding, and when in the opposite direc- 

 tion it is said to be ebbing. The combined flood 

 and ebb movement including the slack water covers 

 on an average 12.42 hours for the semidiurnal cur- 

 rent. If unaffected by a nontidal flow, the flood 

 and ebb movements will each last about 6 hours, 

 but when combined with such a flow, the durations 

 of flood and ebb may be quite unequal . During the 

 flow in each direction the velocity of the current 

 will vary from zero at the time of slack water to 

 a maximum about midway between the slacks. (14) 



REVERSING THERMOMETER (RICHTER REVERSING THER- 

 MOMETER) . 1. A deep-sea recording thermometer. The 

 temperature reading at the desired depth is pre- 

 served by overturning the instrument to break the 

 mercury column. 



Deep-sea reversing thermometers are delicate, 

 but highly accurate, mercurial thermometers special- 

 ly designed for recording water temperatures in 

 situ by being reversed when the Nansen bottle Is 

 tripped by the messenger. There are two types of 

 reversing thermometers, protected and unprotected. 

 The temperature scale is Celsius (Centigrade) and 

 is carefully etched on the glass stem. The scale 

 is read with a thermometer reader, or viewer. Each 

 thermometer actually consists of two parts: one, 

 the reversing thermometer which is called the main; 

 the other, a regular thermometer which is called 

 the auxiliary. (35) 



2. A mercury- in-glass ther- 

 mometer which records temperature upon being in- 

 verted and thereafter retains its reading until 

 returned to the first position. It consists of a 

 conventional bulb connected to a capillary in which 

 a constriction is placed so that upon reversal the 

 mercury column breaks off in a reproducible manner. 

 The mercury runs down into a smaller bulb at the 

 other end of the capillary, which is graduated to 

 read temperature. A 360°turn in a locally widened 

 portion of the capillary serves as a trap to pre- 

 vent further addition of mercury if the ther- 

 mometer is warmed and the mercury expands past the 

 break-off point. 



The remote-reading potentialities of revers- 

 ing thermometers make them particularly suitable 

 for use in measuring temperatures at depths in the 



sea. In this application, both protected ther- 

 mometers and unprotected thermometers are used, 

 each of which is provided with an auxiliary ther- 

 mometer. They are generally used in pairs in 

 NANSEN BOTTLES. They are usually read to .OloC, 

 and after the proper corrections have been applied, 

 their readings are considered reliable to .02oc. 

 Details of the correction procedure are given in 

 Lafond's Tables. (24) 



REVETMENT . A facing of stone, concrete, etc., 

 built to protect a scarp, embankment or shore 

 structure against erosion by wave action or cur- 

 rents. (11) 



RFCWA . Regional Fisheries Commission for Western 

 Africa. , 



RHODAMINE - B . A type of dye used in experiments 

 concerned with determination of diffusion rates 

 for radioactivity in the ocean. (34) 



RIA . A long narrow inlet, with depth gradually 

 diminishing inward. (11) 



RICHARDSON CURRENT METER . The Richardson Current 

 Meter is a device which measures the speed and 

 direction of ocean currents and stores the infor- 

 mation on 16mm film. Its chief elements are a 

 SAVONIUS ROTOR "for measurement of current speed, a 

 vane for determining the current direction rela- 

 tive to the meter, a compass which fixes the posi- 

 tion of the meter itself, a system of fiber optic 

 light pipes which transfer the information to a 

 camera, and the 16mm battery operated camera which 

 can be set to run continuously or intermittently. 

 Under typical operating conditions, data can 

 be recorded by this current meter for periods up 

 to one year. (35) 



RIDGE (WEDGE) . 1. In meteorology, an elongated 

 area of relatively high atmospheric pressure, 

 almost always associated with and most clearly 

 identified as an area of maximum anticyclonic cur- 

 vature of wind flow. The locus of this maximum 

 curvature is called the ridge line. 



Sometimes, particularly in discussions of 

 atmospheric waves imbedded in the WESTERLIES, a 

 ridge line is considered to be a line drawn through 

 all points at which the anticyclonically curved 

 ISOBARS or contour lines are tangent to a latitude 

 circle. 



The most common use of this term is to dis- 

 tinguish it from the closed circulation of a high 

 (or anticyclone); but a ridge may include a high 

 (and an upper-air ridge may be associated with a 

 surface high) and a high may have one or more 

 distinct ridges radiating from its center. (24) 



2. A long, narrow elevation of the sea floor, 

 with steep sides and more irregular topography 

 than a RISE. (26) 



RIDGED ICE . Pressure ice having readily observed 

 surface roughness in the form of a ridge or many 

 ridges. (15) 



RIGHT LAY. See WIRE ROPE. 



RILL MARKS . Tiny drainage channels in a beach 

 caused by the flow seaward of water left in the 

 sands of the upper part of the beach after the 

 retreat of the tide or after the dying down of 

 storm waves. (11) 



RING TRAVEL . Essentially a large, relatively 

 coarse plankton net attached to a strong ring of 

 large diameter and provided with a towing bridle. 



RIP . The agitation of water caused by the inter- 

 action of water currents or by a rapid current 

 setting in over an irregular bottom; for example, 

 a "tide rip." See RIP CURRENTS. (24) 



100 



