MODULUS OF RIGIDITY . Also called Shear Modulus of 

 Elasticity, Modulus of Elasticity in Shear, Tor- 

 sional Modulus of Elasticity and Modulus of Elas- 

 ticity in Torsion. A measure of stiffness of a 

 material subjected to shear loading. Usually the 

 tangent or secant Modulus of Elasticity of a materi- 

 al in the Torsion Test. The relationship between 

 Torsional Stress and Torsional Strain. The tangent 

 modulus may also be obtained from the Torque-Twist 

 Diagram by dividing slope of the straight-line 

 portion by the polar moment of inertia (in. ) of 

 the specimen. For cast iron, where the specimen 

 has been standardized. Modulus of Rigidity is cal- 

 culated by multiplying slope of the Torque-Twist 

 Diagram by 32.2. In the Gehman Torsional Test, 

 Modulus of Rigidity is calculated as follows: 

 0.795 K (180- e) 

 bh3 MS 

 where G " Modulus of Rigidity, psi 



S - total angular deflection, deg 



K - torsional constant of wire, g-cm/deg twist 



b - specimen width, in. 



h "■ specimen thickness, in. 



M ~ factor based on b/h 

 Modulus of Rigidity may also be calculated from 

 Modulus of Elasticity in Tension, Compression or 

 Flexure: 



° 2 (1 + r) 

 where E = Modulus of Elasticity, psi 



r = Poisson's Ratio 

 An Apparent Modulus of Rigidity is sometimes 

 determined for plastics. 



MOHO . A short, popular form of MOHOROVICIC DIS- 

 CONTINUITY. (27) 



MOHQLE . A word coined for use in referring to a 

 project which comprises an attempt to drill, at 

 sea, through the crust of the earth to the 

 MOHOROVICIC DISCONTINUITY. (27) 



MOHOROVICIC DISCONTINUITY . The level at which 

 primary seismic waves suddenly increase to a speed 

 of about 8.1 km. /sec. This boundary is usually 

 taken to indicate the upper limit of the mantle, 

 separating it from the crust above, although it 

 has also been suggested that it may only indicate 

 a change of state and not of material. (27) 



MOISTURE FILM COHESION . See APPARENT COHESION. 



MOLE . In coastal terminology, a massive solid-fill 

 structure of earth, (generally revetted), masonry, 

 or large stone. It may serve as a breakwater or 

 pier. (11) 



MOLECULE . The smallest division of a chemical com- 

 pound which retains all of its chemical properties. 

 Molecules are composed of chemically united atoms; 

 the simplest compounds are composed of only two 

 atoms, other complex compounds are composed of 

 thousands of atoms of many different kinds. (39) 



MOLLUSCS (MOLLUSKS) . Marine animals (usually with 

 shells) significant as fouling forms, including 

 mussels, jingle shells, oysters, and boring forms, 

 such as shipworms and boring clams. (15) 



MONACO OCEANOGRAPHIC INSTITUTION . The Oceano- 

 graphic Institute at 195 Rue St. Jacques, Paris 5, 

 was founded by Prince Albert I of Monaco. The 

 Institute conducts studies on oxygen content of 

 Mediterranean water and on the physiology of fish 

 migration. The Institute is supported by funds ob- 

 tained from the Monaco Museum, and by the Centre 

 Nationale de la Recherche Scientifique. 



MONACO OCEANOGRAPHIC MUSEUM . Founded in 1899 by 

 Prince Albert I of Monaco, "The Prince of Oceano- 

 graphers", this museum is one of the world's most 

 elaborate and finest structures devoted to 

 oceanography. 



MONAXON . See SPICULE. 



MONSOON . A name for seasonal winds (derived from 

 Arabic mausim, a season) . It was first applied to 

 the winds over the Arabian Sea, which blow for six 

 months from northeast and for six months from south- 

 west, but it has been extended to similar winds in 

 other parts of the world . Even in Europe the pre- 

 vailing west to northwest winds of summer have 

 been called the "European monsoon". The primary 

 cause is the much greater annual variation of tem- 

 perature over large land areas compared with neigh- 

 boring ocean surfaces, causing an excess of pres- 

 sure over the continents in winter and a deficit 

 in su mm er, but other factors such as the relief 

 features of the land have a considerable effect. 



The monsoons are strongest on the southern 

 and eastern sides of Asia, the largest land mass, 

 but monsoons also occur on the coasts of tropical 

 regions wherever the planetary circulation is not 

 strong enough to inhibit them. They have been 

 described in Spain, northern Australia, Africa 

 except the Mediterranean, Texas and the western 

 coasts of the United States and Chile. 



In India the term is popularly applied chiefly 

 to the southwest monsoon and, by extension, to the 

 rains which it brings. (24) 



MONSOON CURRENT . A seasonal Indian Ocean current 

 flowing eastward and southeastward across the 

 Arabian Sea and the Bay of Bengal. During the nor- 

 thern hemisphere summer this current forms the nor- 

 thern and northeastern part of the general clock- 

 wise oceanic circulation of the northern part of 

 the Indian Ocean. During the northern hemisphere 

 winter the monsoon current is replaced by a west- 

 ward setting NORTH EQUATORIAL CURRENT. (17) 



MONSOON FOG . An advection type of fog occurring 

 along a coast where monsoon winds are blowing, 

 when the air has a high specific humidity and there 

 is a large difference in the temperature of adjacent 

 land and sea. (17) 



MOORE AND NEILL SAMPLER . This sediment coring 

 device is essentially a protected glass tube 

 through which water flows freely during descent 

 and which is forced by impact into the sediment. 

 On hauling, a simple valve mechanism closes the 

 top of the tube and the sample may be brought to 

 the surface. The body of the sampler is a brass 

 cylinder into which fits a thinner metal tube hold- 

 ing the glass sampling tube. When the glass tube 

 is in position it is closed by a rubber bung which 

 comes hard against the upper surface of the main 

 body of the sampler in the center of which is a 

 hole. Through this hole passes a short piece of 

 small-bore glass tube which in turn passes through 

 the rubber bung closing the glass sampling tube. 

 The upper end of this short glass tube is joined 

 by a rubber to a second similar tube which fits 

 against a simple valve. The latter consists of a 

 flat ground rim on which lies a ground glass plate 

 confined in a cage. As the sampler descends, water 

 streams through the whole device and escapes through 

 the valve, since the glass closing-disc is lifted 

 up in its cage by the upward pressure of the water. 

 The weight of the sampler drives the tube into the 

 bottom and a core of material is forced into the 

 glass sampling tube. The glass plate then drops on 

 to the ground surface (being no longer forced up by 

 the water) and when the device is raised gives a 

 watertight joint. At the upper end of the device 

 is a pillar on which is mounted a propeller which 

 revolves freely and thereby helps to maintain a 

 vertical descent. (35) 



MOORE FREE CORER . This sediment, sampler is de- 

 signed to drop free from a ship to the sea floor, 

 obtain a core and return to the surface leaving its 

 expendable weight and casing embedded in the bottom. 

 The free corer consists of two basic assemblies: 

 (1) a recoverable core barrel, check valve, buoyant 

 chamber assembly filled with gasoline, and (2) an 



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