TIDE CYCLE 



tide cycle — A period which includes a complete 

 set of tide conditions or characteristics, such as 

 a tidal day, a lunar month, or the Metonic cycle. 

 See tidal current cycle. (68) 



FIRST QUARTER 

 NEAP TIDE 



QUADRATURE * 



FULL 

 MOON 



€ 



SPRING 

 TIDE 



QUADRATURE 



SYZYGY 

 (OPPOSITION) 



LAST 

 QUARTER 



c 



NEAP TIDE 



SYZYGY 

 (CONJUNCTION) 



/ ^ V 



^ NEW. ^ 



MOON 



e 



SPRING 

 TIDE 



TIDE CYCLE 



tide gage — A device for measuring the height of 

 tide. It may be simply a graduated staff in a 

 sheltered location where visual observations can 

 be made at any desired time ; or it may consist 

 of an elaborate recording instrument (some- 

 times called marigraph) making a continuous 

 graphic record of tide height against time. Such 

 an instrument is usually actuated by a float in 

 a pipe communicating with the sea through a 

 small hole which filters out shorter waves. 



See automatic tide gage, box gage, pressure 

 gage, tape gage, tide staff. (5) 



tidehead — The inland limit of water affected by 

 a tide. (68) 



tide indicator — A form of tide gage designed for 

 tlie purpose of clearly indicating the height and 

 time of the tide measured from a predetermined 

 plane of reference. 



tideland — Land whicli is under water at high tide 

 and uncovered at low tide. Tideland, Deach, 

 strand, and seashore ha\e neai-ly the same 

 meanings. Tideland refers to the land some- 

 times covered by tidewater. (68) 



tidemark — 1. A liigli water mark left by tidal 

 water. 



2. Tlie highest point reached by a high tide. 



3. A mark placed to indicate the highest point 

 reached by a liigh tide, or occasionally, any 

 specified state of tide. 



(68) 



tide pole — See tide staff. 



tide-predicting machine — An instrument that 

 computes, sometimes for years in advance, the 

 times and heights of high and low waters at a 

 reference station by mechanically summing the 

 harmonic constituents of which the tide is 

 composed. 



tide prediction — Predetermined time and height 

 of high or low water at a reference station. 



May be computed years in advance by mechani- 

 cally summing the harmonic constituents of 

 which the tide is composed. Used to compile 

 tide tables. 



tide-producing force(s) — The slight local differ- 

 ence between the gravitational attraction of two 

 astronomical bodies and the centrifugal force 

 that holds them apart. These forces are exactly 

 equal and opposite at the center of gravity of 

 either of the bodies, but, since gravitational at- 

 traction is inversely proportional to the square 

 of the distance, it varies from point to point on 

 the surface of the bodies. Therefore, gravita- 

 tional attraction predominates at the surface 

 point nearest to the other body, while centrifu- 

 gal "repulsion" predominates at the surface 

 point farthest from the other body. Hence there 

 are two regions where tide-producing forces 

 are at a maximum, and normally there are two 

 tides each hmar day and solar day. (5) 



tide race — A very rapid tidal current in a nar- 

 row channel or passage. 



tide range — The difference in height between con- 

 secutive high and low waters. Wliere the type 

 of tide is diurnal the mean range is the same 

 as the diurnal range. 



See diurnal range, great diurnal range, 

 mean range, apogean range, perigean range, 

 great tropic range, small tropic range, mean 

 tropic range. 



MEAN HIGH WATER SPRINGS 



MEAN HIGH WATER 



MEAN HIGH WATER NEAPS 



MEAN TIDE LEVEL 



MEAN LOW WATER NEAPS 



MEAN LOW WATER 



MEAN LOW WATER SPRINGS 



CHART DATUM 



T 



T~T 



U 



UJ w 



-Z 



,1 -I 



"i| 



zt 

 < I 



TIDE RANGES FROM CHART DATUM 



tide rip — A misnomer for rips, 

 tide rise — See rise (sense 1). 

 tide staff— (also called tide -pole). A tide gage 

 consisting of a vertical graduated staff from 



166 



