REVERSIBLE TRANSDUCER 



motions of the principal attracting body; the 

 least heights are directly under the tide-produc- 

 ing body, on opposite sides of the earth. See 

 direct tide. 



reversible transducer — See bilateral trans- 

 ducer. 



reversing current — (or alternating current^ 

 rectilinear cw^ent). A tidal current that 

 flows alternately in approximately opposite di- 

 rections, with a period of slack water at each 

 reversal of direction. Eeversing currents us- 

 ually occur in rivers and straits where the flow 

 is restricted. When the flow is toward shore, 

 the current is flooding; when in the opposite 

 direction, it is ebbing. 



reversing thermometer — A mercury-in-glass 

 thermometer that records temperature upon 

 being inverted 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 re- 

 producible manner. The mercury runs 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 prevent further 

 addition of mercury if the thermometer is 

 warmed and the mercury expands past the 

 break-off point. 



In measuring temperatures at depths in the 

 sea, both protected thermometers and un- 

 protected thermometers are used, each of 

 which is provided with an auxiliary thermom- 

 eter. They are generally used in pairs on 

 Nansen bottles. They are usually read to 

 0.01 °C, and after the proper corrections have 

 been applied, their readings are considered re- 

 liable to 0.02°C. (Details of the correction 

 procedure are given in LaFond's Tables (H.O. 

 Publication 6U). (5) 



Reynolds number — The nondimensional ratio of 

 the inertial force to the viscous force in fluid 

 motion, 



V 



where L is a characteristic length, v the kine- 

 matic viscosity, and U a characteristic velocity. 

 The Reynolds number is of great importance 

 in the theory of hydrodynamic stability and the 

 origin of turbulence. (6) 



rhabdolith — Minute calcareous bodies contained 

 in deep sea ooze, classed as protozoans by some 

 investigators and as algae by others. (53) 



rheologic settling— The failure of a sediment 

 under load through plastic flow. See rheology. 



rheology— The study of the flow of materials, 

 particularly the plastic flow of solids. (2) 



rhizoid — A unicellular or uniseriate rootlike fila- 

 ment sei-ving for attachment of algae. (13) 



'^ixmx.^^ 



RHABDOUTHS (X 2000) 



(SHROCK & TWENHOFEl. 1933) 



rhizome — A rootlike stem that creeps just below 

 the surface of the bottom, bearing at the nodes 

 erect stems or leaves and one or more roots. 



rhodamine B dye — A synthetic red or pink dye 

 sometimes used as a tracer in studies of flow of 

 water, turbulence, pollution, etc., in rivers, estu- 

 aries, and the ocean. 



rhumb line — (or loxodrome). A curve which 

 crosses all meridians at a constant angle. (37) 



ria — Any broad river opening into the ocean. Not 

 necessarily a submerged river mouth or open 

 valley in a mountainous coast. 



ria coast — A coast having drowned river valleys 

 characterized by long fiordlike bays which have 

 few branches. The bays differ from fiords in 

 origin and are shorter, shallower, and more 

 funnel shaped, broadening and deepening sea- 

 ward. The type example is northwestern Spain. 



(2) 

 Richter magnitude scale — See magnitude (sense 



1). 



ride-up — See run-up. 



ridge — A long, narrow elevation of the sea floor 

 with steep sides and irregular topography. (62) 



ridged ice — Pressure ice in linear formation. 



ridging — The process that leads to the formation 

 of ridged ice. (6.5) 



rift valley — See fault block. 



rill mark — A small groove, furrow, or channel 

 made in mud or sand on a beach by tiny streams 

 following an outflowing tide. (2) 



rip current — The return flow of water piled up on 

 shore by incoming waves and wind; a strong 

 narrow surface current flowing away from the 

 shore. A rip current consists of three parts: 

 the feeder current flowing i^arallel to the shore 

 inside the breakers ; the neck, where the feeder 

 currents converge and flow through the breakers 

 in a narrow band or "rip" ; and the head, where 

 the current widens 'and slackens outside the 



136 



