the mesh. Deep tows and simultaneous collections 

 are not considered practical with this sampler. 

 (35) 



METEOROLOGICAL EQUATOR . See EQUATORIAL TROUGH. 



METEOROLOGICAL TIDES . Tidal constituents having 

 their origin in the daily or seasonal variations 

 in weather conditions which may occur with some 

 degree of periodicity. The principal meteoro- 

 logical constituents recognized in the tides are 

 Sa, Ssa, and Sj^. (14) 



METEOROLOGY . The study dealing with the phenomena 

 of the ATMOSPHERE. This includes not only the 

 physics, chemistry, and d3mamics of the atmosphere, 

 but is extended to include many of the direct ef- 

 fects of the atmosphere upon the earth's surface, 

 the oceans, and life in general. The goals often 

 ascribed to meteorology are the complete understand- 

 ing, accurate prediction, and artificial control 

 of atmospheric phenomena. 



A distinction can be drawn between meteorology 

 and climatology, the latter being primarily con- 

 cerned with average, not actual, weather conditions. 

 Meteorology may be subdivided, according to the 

 methods of approach and the applications to human 

 activities, into a large number of specialized 

 sciences. The following are the most generally 

 recognized: aerology, aeronomy, aeronautical 

 meteorology, agricultural meteorology, applied 

 meteorology, dynamic meteorology, hydrometeorology, 

 physical meteorology, radio meteorology, synoptic 

 meteorology, macrometeorology, mesometeorology, 

 micrometeorology. (12) 



METONIC CYCLE . A period of 19 years or 235 luna- 

 tions. Devised by Meton, an Athenian astronomer 

 who lived in the fifth century before Christ, for 

 the purpose of obtaining a period in which new and 

 full moon would recur on the same day of year. 

 Taking the Julian year of 365.25 days and the 

 synodic month as 29.530588 days, we have the 19- 

 year period of 6939.75 days as compared with the 

 235 lunations of 6939.69 days, a difference of 

 only 0.06 day. (14) 



MEYER-OVERTON THEORY . A physiological concept 

 that relates the narcotic action of certain gases 

 directly to their comparative solubility in fat 

 and water. (37) 



MHA . U. S. Navy ship designation for a Mine Hun- 

 ter, Auxiliary. 



MHC . U. S. Navy ship designation for a Mine Hunter, 

 Coastal. 



MHD . Magnetohydrodynamics . 



MHO . The unit of conductance. It is equal to the 

 reciprocal of resistance. (36) 



MICROAEROPHILES . Those bacteria which require a 

 reduction of free oxygen, but not to the point of 

 , anaerobic conditions. (13) 



MICROWAVE POSITION-FIXING . A navigation system, 

 developed by the National Research Council of 

 Canada, capable of measuring bearing in 0.02° in- 

 crements to three shore based unattended transmit- 

 ters. On the ship is a rotary radar type antenna 

 that scans the signals from the three shore sta- 

 tions. Equipment design aboard the ship permits a 

 three point fix type of plot. (29) 



MID-CHANNEL BUOY . A buoy marking the middle of a 

 channel. (17) 



MIDDLE GROUND BUOY . A buoy marking a shoal with 

 channels on both sides. (17) 



MID-EXTREME TIDE . A plane midway between the ex- 

 treme high water and the extreme low water occur- 

 ring in any locality. (14) 



MIDWATER TRAWL . The Isaacs-Kidd Midwater Trawl was 

 developed at the University of California, Scripps 

 Institution of Oceanography. It is capable of col- 

 lecting some of the larger and more active animal 

 forms found in the ocean. As implied by its name, 

 the trawl was primarily designed for use in mid- 

 water, that is, ocean water below the surface layers. 

 An ordinary net will surface behind the towing ves- 

 sel unless hauled at extremely slow speeds. To 

 counteract this tendency, the midwater trawl has an 

 inclined plane surface rigged in a manner opposite 

 to the elevating action of a kite surface. 



The Midwater Trawl has been manufactured with 

 both a 10- and 15-foot mouth, and in 31- and 72- 

 foot lengths, respectively. (35) 



MILL I . A prefix indicating one-thousandth. 



MILLIGAL . A measure of gravity equal to 1 thousand- 

 th part of a GAL. 



MINIATURE CURRENT METER . The passage of current 

 past a probe on each blade of a propeller type, 

 or each cup of a PRICE type meter can be detected 

 by the change of electrical resistance between 

 that probe and a distant electrode. A voltage 

 pulse is produced as each blade passes the elec- 

 trode the pulse rate which depends on the velocity 

 of the current is indicated on a milliammeter. 



An oscillator supplies, via a cathode follower, 

 a wheats tone bridge network of which the probe im- 

 pedance forms one arm. Any out of- balance signal 

 from the bridge is filtered, amplified and rectified. 

 After removal of the carrier frequency the signal 

 is again amplified and drives an electronic fre- 

 quency meter which in turn drives the Indicating 

 meter and recorder. The indicating meter may be 

 connected to the second amplifier for the initial 

 balancing of the bridge. (30) 



MINIMUM FLOOD . See FLOOD CURRENT. 



MINLANT . Mine Warfare Forces, Atlantic (USN) . 



MINOR LOBES . (See LOBES). 



MINPAC . Mine Warfare Forces, Pacific (USN). 



MICROBAR . A microbar is a unit of pressure common- 

 ly used in acoustics. One microbar is equal to 1 

 dyne/cm^. (1) 



MICRODIST. See ELECTROTAPE. 



MICROPHONE . A microphone is an electroacoustic 

 transducer that responds to sound waves and 

 delivers essentially equivalent electric waves. (1) 



MICROPLANKTON . See MARINE LIFE. 



MICROSPORE . A spore which germinates to form the 

 male gametophyte. (18) 



MISTRAL . A cold, dry wind blowing from the north 

 over the northwest coast of the Mediterranean Sea, 

 particularly over the Gulf of Lion. Also called 

 cierzo. (17) 



MIXED CURRENT . Type of tidal current characterized 

 by a conspicuous velocity difference between the 

 two floods or two ebbs usually occurring each tidal 

 day. See MIXED TIDE. (14) 



MIXED LAYER . In oceanography, the surface layer 

 of virtually isothermal water, which frequently 

 exists above the THERMOCLINE. (12) 



MIXED TIDE . Type of tide in which the presence of 



76 



