elastic strain when subjected to an external mag- 

 netic field. Also, magnetostriction is the con- 

 verse phenomenon in which mechanical stresses cause 

 a change in the magnetic induction of a ferromag- 

 netic material. (1) 



MAGNETOSTRICTION TRANSDUCER . A magnetostriction 

 transducer is a transducer that depends for its 

 operation on the interaction between the mag- 

 netization of the deformation of a material having 

 magnetostrlctive properties. (1) 



MAJOR LOBES . (See LOBES) 



MALKUS BATHYPITOTMETER . A pitot-type current 

 meter, devised by Willem Malkus, having the shape 

 of a large BATHYTHERMOGRAPH, which responds to cur- 

 rents in the range 50 to 250 cm/sec. It is neces- 

 sary to move the ship ahead slowly if the current 

 speeds do not fall in this range and then allow 

 the instrument to come to equilibrium at each of 

 a succession of depths to obtain readings. Read- 

 ings on two headings must be made and compared to 

 evaluate the resultant velocity at each level if 

 this is not known at the start or if the current 

 turns with depth. (32) 



MAMOS . Marine Automatic Meteorological Oceano- 

 graphic Station. 



MANOMETER . An instrument for measuring pressure 

 of gases and vapors both above and below atmos- 

 pheric pressure. 



MAP . An inshore navigation system employing a 

 good quality Radar as a part of the system. This 

 radar is modified to give a high precision range 

 accuracy and a selective azimuth control so that 

 only the desired shore targets are indicated. 

 These shore targets are mutually perpendicular 

 screens mounted on the top of a tower. Two or 

 more targets may be located ashore (or on the 

 water) to cover the survey area. 



An automatic plotter fastened over the boat- 

 sheet automatically follows the course of the 

 vessel over the sheet. The ship's position can 

 be pricked into the boat-sheet or observed through 

 cross hairs. The ship's distance from both targets 

 is also printed on a tape at any time of command. 

 (29) 



MARAD . Maritime Administration. 



MARES ' TAILS . Long slender streaks of cirrus thick- 

 ening into cirrostratus, and then gradually lower- 

 ing into watery altostratus. (17) 



MARIGRAM . A graphic representation of the rise 

 and fall of the tide in which time is represented 

 by the abscissas and the height of the tide by 

 ordinates, particularly the record traced by a 

 marigraph; a tide curve. (17) 



MARINE CLIMATE . The type of climate characteristic 

 of coastal areas, islands, and the oceans, the dis- 

 tinctive features of which are small annual and 

 daily temperature range and high relative humidity, 

 in contrast with continental climate, which is 

 characteristic of the interior of a large land mass, 

 and the distinctive features of which are large 

 annual and daily temperature range and dry air with 

 few clouds . (17) 



MARINE LIFE . Classified upon the basis of common 

 habits of locomotion and mode of life, and upon 

 common ecological distribution the population of 

 the sea may be divided into three large groups. 

 These are: (1) Benthos, which includes the sessile, 

 creeping, and burrowing organisms found on the bot- 

 tom of the sea, with representatives of the group 

 extending from the high-tide level down into the 

 abyssal depths. The benthos comprises (a) sessile 

 animals, such as the sponges, barnacles, mussels, 

 oysters, crinoids, corals, hydroids, bryozoa, some 



of the worms, all of the seaweeds and eel grass, 

 and many of the diatoms, (b) creeping forms, such 

 as crabs, lobsters, certain copepods, amphipods , 

 and many other Crustacea, many protozoa, snails, 

 and some bivalves and fishes, and (c) burrowing 

 forms, including most of the clams and worms, some 

 Crustacea, and echinoderms. (2) Nekton, which is 

 composed of swimming animals found in the pelagic 

 division. In this group are included most of the 



adult squids, fishes, and whales namely, all of 



the marine animals that are able to migrate freely 

 over considerable distances. Obviously, there are 

 no plants in this general group. (3) Plankton, 

 which includes all of the floating or drifting life 

 of the pelagic division. The organisms, both plant 

 and animal, of this division are usually micro- 

 scopic or relatively small; they float more or less 

 passively with the currents and are therefore at 

 the mercy of prevailing water movements. Many of 

 the animals are able to make some progress in 

 swimming, although their organs of locomotion are 

 relatively weak and ineffective. 



The plankton is divided into two main divi- 

 sions: (A) Phytoplankton, which comprises all of 

 the floating plants, such as diatoms, dinoflagel- 

 lates , coccolithophores , and sargassum weeds. (B) 

 Zooplankton, which includes (a) myriads of animals 

 that live permanently in a floating state, and (b) 

 countless numbers of helpless larvae and eggs of 

 the animal benthos and nekton. On the basis of 

 size the plankton may be further subdivided as 

 follows: (C) Macroplarikton, includes those or- 

 ganisms of about 1 ram in length which can be caught 

 with a' net of No. 00 or 000 bolting cloth. (D) 

 Mesoplankton, includes those organisms between 1 mm 

 and 1 cm, but is infrequently used because of pos- 

 sible confusion with the use of the same term to 

 indicate those plankton living at mid-depth. (E) 

 Megaloplankton, occasionally used to indicate the 

 largest plankton forms. (F) Microplankton, also 

 in part called Net Plankton, is that which is com- 

 posed of individuals below about 1 mm in size, but 

 yet large enough to be retained by a net of No. 20 

 bolting cloth with a mesh aperture of about 0.076 

 mm. (G) Nannoplankton, comprises many of the very 

 small forms (about 5 to 60) which must be collected 

 by centrifuging the water. (H) Ultraplankton, 

 includes those organisms smaller than the nanno- 

 plankton. 



The planktonic eggs and larvae of the benthos 

 and nekton make up what is known collectively as 

 the Temporary Plankton, or Meroplankton. That 

 part of the plankton which is made up of animals 

 living their complete life cycle in the floating 

 state is called the Permanent Plankton, or Holo- 

 plankton. The term Hypoplankton is sometimes used 

 to indicate those forms whose swimming power puts 

 them somewhere in between the plankton and nekton, 

 such as some mysids, amphipods, cumacids, etc. 

 which live both on or near the bottom. (13) 



MARINE METEOROLOGY . That part of meteorology which 

 deals mainly with the study of oceanic areas, in- 

 cluding island and coastal regions. In particular 

 it serves the practical needs of surface and air 

 navigation over the oceans. 



Since there is a close interaction between 

 ocean and atmosphere, and oceanic influences upon 

 weather and climate can be traced far inland over 

 the continents, modern meteorology uses this name 

 mainly for making regional or administrative dis- 

 tinctions. (12) 



MARINE RAINBOW . A rainbow seen in ocean spray, 

 sometimes called sea rainbow. (17) 



MARINE SEDIMENTS . Marine sediments are subdivided 

 into two major groups, termed PELAGIC and TER- 

 RUGENOUS . The pelagic deposits are those found 

 in deep water far from shore and may be predomi- 

 nantly either organic or inorganic in origin. They 

 are light-colored, reddish or brown, fine-grained 

 and, generally, they contain some skeletal remains 



T2 



