lower parts of the central tube is a plug held in 

 position by retaining hooks through slots in the 

 wall of the lower tube. I'Jhen the device strikes 

 the bottom a mouth tube rises, disengaging the 

 plug, which flies up the tube. The water pressure 

 then forces material up into the collecting tube. 

 (35) 



HOLME (SUCTION GRAB) 



SAMSON 

 SECURINC UD 



HOLME MUD SAMPLER . With this device the sample is 

 taken by a scoop rotating on an axle mounted on a 

 heavy frame that rests firmly on the bottom. The 

 device is lowered open with the entire weight 

 being taken by a shackle on a balanced arm. Closure 

 is not effected on touching bottom. On hoisting, 

 the pressure of water on a vane attached to the 

 balanced arm tips a lever and allows a pin to slip 

 out and release the shackle. The weight is then 

 transferred to a rope rotating round a large drum. 

 This in turn rotates a small pulley and drags the 

 sampling hemisphere through the bottom via a second 

 pulley to which it is attached by a light wire. The 

 maximum volume of the sample is 5 1/2 liters, and 

 in practice, usually about 3-4 liters are collected. 

 (35) 



HOLOPHYTIC . Obtaining food after the manner of a 

 green plant. (20) 



HOLOPLAMCTON . See MARINE LIFE. 



HOLOZOIC . Obtaining food after the manner of most 

 animals by ingesting complex organic matter. (20) 



HOMOIOTHERMOUS . Warm-blooded animals having regu- 

 lated body temperatures. Seals, whales and other 

 marine mammals have deep layers of fat (blubber) 

 under the skin that insulates their bodies from 

 heat loss in the water. (19) 



HORS E LATITUDES . The regions of calms and variable 

 winds coinciding with the subtropical high pressure 

 belts on the poleward sides of the trade winds. 

 The expression is generally applied only to the 

 northern of these two regions in the North Atlantic 

 Ocean, or to the portion of it near Bermuda. (17) 



HOT-WIRE INSTRUMENT FOR MEASURING LOW VELOCITIES . 

 The probe incorporates a thermocouple to measure 

 the temperature, made from two metals which form a 

 tubular thcrmojunction. The hot wire, a nichrome 

 resistance wire is mounted in a small metal tube at 

 the tip of the probe. The wire is heated by an 

 electric current which is passed through it from 

 the adjustable current supply. The temperature 

 difference between the probe and the water is 

 measured by a pair of thermojunctions . A sleeve 

 joint in the tube made from copper and constan- 

 tan, forms the hot junction and gives a voltage 

 dependant on the temperature of the tube. The cold 

 junction is placed clear of the probe, but in the 

 water, giving a voltage dependent on the tempera- 

 ture of the water. The difference between the vol- 

 tages from the junctions is proportional to the tem- 

 perature difference between them: Eq = K^At 



The cooling effect of the flowing water is 

 most marked at low velocities, becoming less effec- 

 tive as the velocity increases. 



The output voltage is observed on a galva- 

 nometer. For more accurate measurements a D.C. 

 slide wire potentiometer employed in conjunction 

 with the galvanometer is used. (30) 



HOT-WIRE INSTRUMENT FOR OCEAN TURBULENCE 

 MEASUREMENTS . In this system the temperature of 

 the wire is maintained as nearly constant as is 

 possible by increasing the power to the hot-wire 

 when it attempts to cool off and decreasing the 

 power when it attempts to become hotter. If the 

 temperature of the wire is kept constant by means 

 of a negative feedback amplifier which compensates 

 for the cooling effect of the turbulent flow, the 

 wire resistance will remain constant and the heat- 

 ing current in the wire will vary. This variation 

 in the heating current can be used to measure the 

 turbulent fluctuations. The changes in temperature 

 and resistance of the wire are detected by means of 

 a bridge in which the hot-wire forms one of the 

 arms. The wire is made of platinum-coated tungsten 

 one inch long. 



The turbulence signals from the hot-wire are 

 recorded on tape using a frequency modulation sys- 

 tem. A carrier frequency of lOkc is used and the 

 signal from the hot-wire is superimposed on the 

 carrier. The tapes are played back and analyzed 

 on an audio frequency spectrum analyser to obtain 

 the frequency spectrum. (30) 



HOVERCRAFT AND GEMS (GROUND EFFECT MACHINES) . 

 Ships designed to hover above water and supported 

 by air trapped between the bottom of the ship and 

 the water. The supporting air cushion is augmented 

 at high speeds (i.e., 100 knots) by the forward 

 motion of the craft. (Note: Various types of ground 

 effect machines are: Air Curtain, Plenum, Ram Wing, 

 Diffuser-Recirculation, Water Curtain, and Skegs.) 



HUK. 



Hunter-Killer Naval Force or Unit. 



HOMOLOGY . Fundamental similarity; structural like- 

 ness of an organ or part in one kind of animal with 

 the comparable unit in another resulting from des- 

 cent from a common ancestry. (19) 



HOOK . A spit or narrow cape, turned landward at 

 the outer end, resembling a hook in form. (11) 



HOOKAH. In free diving-apparatus consisting of a 

 demand regulator worn by the diver and a hose con- 

 nected to a compressed air supply at the surface. 



HORN BUOY . A buoy provided with a horn. (17) 



HUKFORLANT . Hunter-Killer Forces , Atlantic (USN) . 



HUMBOLDT CURRENT . See PERU CURRENT. 



HUMMOCKED ICE . Ice piled haphazardly into mounds 

 or hillocks. At the time of formation hummocked 

 ice is similar to RAFTED ICE except that the for- 

 mer requires a greater degree of pressure and heap- 

 ing than the latter. After hummocked ice and 

 rafted ice have been repeatedly covered with snow 

 and weathered, no distinction is then made between 

 the two terms and hummocked ice is the term applied 

 to both types. 



HUMMOCKY FLOE. See FLOE. 



57 



