MARS Transponder 



on the distribution curve where 16 and 84 percent 

 of the sample by weight is coarser) and a vertical 

 line through the median diameter of the sample, (11) 



MARSH . A tract of soft, wet or periodically in- 

 undated land, generally treeless and usually 

 characterized by grasses and other low growth. 

 (11) 



MARSH, SALT . A MARSH periodically flooded by salt 

 water. (11) 



MAS CARET. See BORE. 



MASS TRANSPORT . The net transfer of water by wave 

 action in the direction of wave travel. (11) 



MEAN DIURNAL HIGH WATER INEQUALITY . 

 INEQUALITY . 



See DIURNAL 



MEAN HIGHER HIGH WATER (MHHW) . The average height 

 of the higher high waters over a 19-year period. 

 For shorter periods of observations, corrections 

 are applied to eliminate known variations and 

 reduce the result to the equivalent of a mean 19- 

 year value. (14) 



MEAN HIGH WATER (MHW) . The average height of the 

 high waters over a 19-year period . For shorter 

 periods of observations, corrections are applied 

 to eliminate known variations and reduce the result 

 to the equivalent of a mean 19-year value. 



All high water heights are included in the 

 average where the type of tide is either semidiurnal 

 or mixed. Only the higher high water heights are 

 included in the average where the type of tide is 

 diurnal. So determined, mean high water in the 

 latter case is the same as MEAN HIGHER HIGH WATER. 

 (14) 



MEAN HIGH WATER SPRINGS . The average height of the 

 high waters occurring at the time of spring tide. 

 Frequently abbreviated to High Water Springs. (11) 



MEAN LOWER LOW WATER (MLLW) . Frequently abbre- 

 viated lower low water. The average height of the 

 lower low waters over a 19-year period. For short- 

 er periods of observations, corrections are applied 

 to eliminate known variations and reduce the result 

 to the equivalent of a mean 19-year value. (14) 



MEAN LOW WATER (MLW) . The average height of the 

 low waters over a 19-year period. For shorter 

 periods of observations, corrections are applied 

 to eliminate known variations and reduce the result 

 to the equivalent of a mean 19-year value. 



All low water heights are included in the 

 average where the type of tide is either semidiur- 

 nal or mixed . Only the lower low water heights 

 are included in the average where the type of tide 

 is diurnal. So determined, mean low water in the 

 latter case is the same as mean lower low water. 

 (11) 



MAXIMAL BREATHING CAPACITY . The greatest respira- 

 tory minute volume which a person can produce dur- 

 ing a short period of extremely forceful breathing. 

 In healthy young men, it may average as much as 170 

 liters per minute. (37) 



MAXIMUM FLOOD . See FLOOD CURRENT. 



MAXIMUM SOUND PRESSURE . The maximum sound pressure 

 for any given cycle of a periodic wave is the max- 

 imum absolute value of the instantaneous sound pres- 

 sure occurring during that cycle. (2) 



MBA . Marine Biological Association. 



MBL . Marine Biological Laboratory (Woods Hole, 

 Massachusetts) . 



MCS . U. S. Navy designation for a Mine Warfare 

 Command & Support Ship. 



MEAN DEPTH . The average depth of the water area 

 between the still water level and the SHOREFACE 

 profile from the water-line to any chosen distance 

 seaward. (27) 



MEAN DIAMETER. GEOMETRIC . The diameter equivalent 

 of the arithmetic mean of the logarithmic frequen- 

 cy distribution. In the analysis of beach sands it 

 is taken as that grain diameter determined graphi- 

 cally by the intersection of a straight line 

 through selected boundary sizes (generally points 



MEAN LOW WATER SPRINGS (MLWS) . Frequently abbre- 

 viated low water springs. The average height of 

 low waters occurring at the time of the spring 

 tides. It is usually derived by taking a plane 

 depressed below the half-tide level by an amount 

 equal to one-half the spring range of tide, neces- 

 sary corrections being applied to reduce the result 

 to a mean value. This plane is used to considerable 

 extent for hydrographic work outside of the United 

 States and is the plane of reference for the 

 Pacific approaches to the Panama Canal. (14) 



MEAN RANGE OF TIDE (Mn) . The difference in height 

 between mean high water and mean low water. (14) 



MEAN RISE INTERVAL (MRI) . The average interval 

 between the transit of the moon and the middle of 

 the period of the rise of the tide. It may be com- 

 puted by adding the half of the duration of rise to 

 the mean low water interval, rejecting the semidiur- 

 nal tide period of 12.42 hours when greater than 

 this amount. The mean rise interval may be either 

 local or Greenwich according to whether it is re- 

 ferred to the local or Greenwich transit. (14) 



MEAN RISE OF TIDE . The height of mean high water 

 above the plane of reference or datum of chart. 

 (14) 



MEAN RIVER LEVEL . The average height of the sur- 

 face of a river at any point for all stages of the 

 tide over a 19-year period, usually determined from 



74 



