LSD . U. S. Navy designation for a Dock Landing ' 

 Ship. 



LSM. U. S. Navy designation for a Medium Landing 

 Ship. 



meridian of a place. The mean lunar day is ap- 

 proximately 24. 8A solar hours in length, or 1.035 

 times as great as the mean solar day. (14) 



LUNAR MONTH . Same as SYNODICAL MONTH. 



LSMR . U. S. Navy designation for a Medium Landing 

 Ship (Rocket). 



LST. U. S. Navy designation for a Tank Landing 

 Ship. 



LSV . U. S. Navy designation for a Vehicle Landing 

 Ship. 



LUBBER'S LINE . A reference line on any direction- 

 indicating instrument, marking the reading which 

 coincides with the heading. (17) 



LUNAR DAY . The time of the rotation of the earth 

 with respect to the moon, or the interval between 

 two successive upper transits of the moon over the 



LUNAR TIDE . That part of the tide on the earth 

 due solely to the moon as distinguished from that 

 part due to the sun. (14) 



LUNISOLAR TIDES . Harmonic tidal constituents Kx 

 and K2, which are derived partly from the develop- 

 ment of the LUNAR TIDE and partly from the SOLAR 

 TIDE, the constituent speeds being the same in 

 both cases. Also the lunisolar synodic fortnightly 

 constituent MSf. (14) 



LUTITE. Material of grain size less than 4 microns. 

 This term may be used instead of clay, to avoid 

 mineralogical implications. (27) 



LW. 



LOW WATER. 



M 



MA. 



Maritime Administration. 



MAB. The Materials Advisory Board of the National 

 Academy of Sciences - National Research Council. 



MACKEREL SKY . An area of sky with a formation of 

 rounded and isolated cirrocumulus or altocumulus 

 resembling the pattern of scales on the back of a 

 mackerel. (17) 



MACRO PLANKTON . See MARINE LIFE. 



MAD . 1. Magnetic Airborne Detection. 

 2. Magnetic Anamoly Detection. 



MADREPORE . A stony coral which often forms an 

 important building material for reefs. (17) 



MAELSTROM . Famous whirlpool off the Coast of Nor- 

 way in the Lofoten Islands between Moskenesoy and 

 Mosken. (14) 



MAESTRO . 



A northwesterly wind with fine weather 



which blows, especially in summer, in the Adriatic; 

 it is most frequent on the western shore, and is 

 equivalent to the ETESIANS of the eastern Mediter- 

 ranean. It is also found on the coasts of Corsica 

 and Sardina. (12) 



A naturally occurring liquid molten mass, 



MAGM\ . 



the molten material from which igneous rocks are 



formed by solidification. (27) 



MAGNETIC ANOMALY . Variation of the measured mag- 

 netic pattern from a theoretical or empirically 

 smoothed magnetic field on the earth's surface. 

 (27) 



MAGNETIC EFFECT . Phenomenon exhibited by certain 

 metals, particularly nickel and its alloys, which 

 change in length when magnetized, or, (Villari 

 effect) when magnetized and then mechanically dis- 

 torted, undergo a corresponding change in mag- 

 netization. (5) 



MAGNETIC ELEMENTS . Consist of the declination (D) , 

 the horizontal intensity (H) , the vertical inten- 

 sity (Z) , the total intensity (F) , the inclination 

 or dip (I) , the strength of the force toward geo- 



graphic north (X), and the strength of the force 

 toward geographic east (Y) . (27) 



MAGNETIC EQUATOR . An imaginary line passing through 

 the points on the earth's surface where the earth's 

 magnetic field is parallel to the earth's surface 

 (i.e., the inclination is zero). (27) 



MAGNETIC MERIDIAN (GEOMAGNETIC MERIDIAN) . The 

 horizontal line which is oriented, at any specified 

 point on the earth's surface, along the direction 

 of the horizontal component of the earth's magnetic 

 field at that point; not to" be confused with 

 ISOGONIC LINE. (24) 



MAGNETIC NORTH . At any point on the earth's sur- 

 face, the horizontal direction of the earth's mag- 

 netic lines of force (direction of a MAGNETIC 

 MERIDIAN) toward the north magnetic pole, i.e., a 

 direction indicated by the needle of a magnetic 

 compass. Because of the wide use of the magnetic 

 compass, magnetic north, rather than TRUE NORTH, 

 is the common 0° (or 360°) reference in much of 

 navigational practice, including the designation 

 of airport runway alignment.. A heading or course 

 toward magnetic north would be written: 0° mag. 

 See also ACLINIC LINE. (24) 



MAGNETIC PICKUP ROTOR . See SAVONIUS ROTOR. 



MAGNETIC POLE (DIP POLE) . 1. In geomagnetism, 

 either of the two points on the earth's surface 

 at which the MAGNETIC MERIDIANS converge, i.e., 

 where the magnetic field is vertical. 



The exact locations of these two magnetic 

 poles shift in complex fashion. The north magnetic 

 pole is now about 200 miles north of the Boothia 

 Peninsula in Canada, while the south magnetic pole 

 is in South Victoria Land on the Antarctic conti- 

 nent. The two poles do not lie at extremes of a 

 diameter of the earth, for the line joining them 

 misses the exact center of the earth by about 750 

 miles . 



2. In magnetic theory, a fictitious entity 

 analogous to a unit electric charge of electro- 

 static theory. In nature only dipoles, not iso- 

 lated magnetic poles, exist. (24) 



MAGNETOMETER . An instrument for measuring: 



1. Any magnetic element. 



2. The variations in the earth's magnetic 

 field. See also NUCLEAR RESONANCE MAGNETOMETER. 



MAGNETOSTRICTION . Magnetostriction is the phenom- 

 enon wherein ferromagnetic materials experience an 



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