regenerative action is dependent upon the transit 

 time of the signal pulse and is therefore a measure 

 of the propagation velocity. (30) 



VELOCITY GRADIEMT . Gradual changes in the velocity 

 of propagation with distance within a single medium 

 are known as velocity gradients. (4) 



VELOCITY HYDROPHONE . A velocity hydrophone is a 

 hydrophone in which the electric output substan- 

 tially corresponds to the instantaneous particle 

 velocity in the impressed sound wave. (1) 



VELOCITY LEVEL . The velocity level, in decibels, 

 of a sound is 20 times the logarithm to the base 10 

 of the ratio of the particle velocity of the sound 

 to the reference particle velocity. The reference 

 particle velocity shall be stated explicitly. (2) 



VELOCITY OF SOUND . Sound velocity in the ocean 

 varies roughly between 4800 feet per second (fps) 

 and 5100 fps. At 70°F and with a normal salinity 

 of 34 parts per thousand by weight, the sound 

 velocity is 4935 fps at the ocean surface. (Speed 

 of sound in air " 1090 ft. /sec). 



VIBROTRON . A pressure sensing transducer which 

 converts hydrostatic pressure directly into an FM 

 signal which can then be TELEMETERED. 



VIGIA . A rock or shoal the existence or position 

 of which is doubtful, or a warning note to this 

 effect on a chart. (17) 



VISCOSITY . The resistance of liquids, semi solids, 

 and gases to movement or flow. 



VISCOUS DAMPING . Viscous damping is the dissipa- 

 tion of energy that occurs when a particle in a 

 vibrating system Is resisted by a force whose mag- 

 nitude is a constant independent of displacement 

 and velocity, and whose direction is opposite to 

 the direction of the velocity of the particle. (2) 



VITAL CAPACITY . The term for the greatest volume 

 of air that a man can expel from his lungs after 

 a full inspiration. In other words, it is the 

 greatest volume of air that can be moved in and out 

 of the lungs in a single breath. The average man's 

 vital capacity is between 4 and 5 liters. (37) 



VENTRAL . Toward the lower side or belly; away 

 from the back. Opposite to DORSAL. (19) 



VERTEBRATE . An animal having a segmental "back- 

 bone" or vertebral column. (19) 



VIBRATING CORING TUBE . A sediment coring tube 

 designed to vibrate in such a way as to overcome 

 the resistance of compacted ocean floor sediments, 

 sands and gravel. 



VIBRATING WIRE TRANSDUCER . A device that can be 

 used to measure ocean depth. The vibrating element 

 is simply a very fine tungsten wire which is 

 stretched in a magnetic field. The wire vibrates 

 at some precise frequency which is determined by 

 the length and tension of the wire. Pressure 

 changes by varying the tension in the wire change 

 the vibration frequency of the wire. (35) 



VIBRATION . Vibration is an oscillation wherein the 

 quantity is a parameter that defines the motion of 

 a mechanical system. (2) 



VIVIPAROUS . See OVIPAROUS. 



VU . Very Low Frequencies (10-30 kilocycles) . 



VNIRO. All-Union Research Institute of Marine 

 Fisheries and Oceanography (USSR). 



VOLCANIC ASH . Usually fine-grained material 

 ejected by a volcano. Volcanic ash is classed as 

 sand on bottom sediment charts. 



VOLTAIC CELL . A cell consisting of two electrodes 



and one or more eletrolytes which, when connected 



in a closed circuit, will give out electrical energy. 



VOLUME VELOCITY . Volume velocity is the rate of 

 alternating flow of the medium through a specified 

 surface due to a sound wave. (2) 



VOLUNTARY APNEA. See BREATH HOLDING. 



w 



WAFC . West African Fisheries Commission. 



WARP . To move, as a vessel, from one place to 

 another by means of lines fastened to an object, 

 such as a buoy, wharf, etc., secured to the ground. 

 (17) 



WARPING BUOY . A buoy so located that lines to it 

 can be used for the movement of ships. 



WASH AND STRAIN ICE FOOT . An ice foot formed from 

 ice casts and slush and attached to a shelving 

 beach, between the high and low water lines. High 

 waves and spray may cause it to build up above the 

 high water line. (17) 



WATCH BUOY . See STATION BUOY. 



WATER CLARITY METER (MOVABLE DISC TYPE) . A visual 

 photometer consisting of two discs of different 



colors and sizes connected by a vertical shaft. 

 The upper (gray, smaller) disc slides on the shaft 

 so that it can be lifted above the fixed, lower 

 (white, larger) disc by an auxiliary line. The 

 upper disc is separated from the lower disc until 

 the two appear to be equally luminous. Once the 

 two are properly separated they will continue to 

 match in homogeneous water regardless of the depth 

 to which the apparatus is submerged . 



The separation of the discs is a direct mea- 

 sure of the clarity of the water and can be con- 

 verted to hydrological range by a multiplying fac- 

 tor. The hydrological range is that range at which 

 the apparent contrast is two per cent; the apparent 

 contrast is a function of the reflectivities of the 

 two discs, their average depth, and the angle of 

 sight to the discs. (35) 



WATER CLARITY METER (PHOTOCELL TYPE) . This meter 

 was developed to permit underwater visibility read- 

 ings by swimmers . It will measure and record sur- 

 face illumination, the decrease of ambient light 

 with depth, the attenuation of illumination of a 

 beam of light beneath the surface, and the depth 

 of the instrument. The underwater unit contains 

 an Alpha-meter, which is a light source at a fixed 

 distance from a photocell, to provide a measure of 

 the attenuation of the beam of light; an h-meter. 



126 



