supported by net floats. The indicator case is 

 clear lucite. It contains the indicating meter and 

 electric circuitry for temperature determination. 

 It also contains a Veeder-Root counter which indi- 

 cates directly in centimeters the depth at which 

 the sensing unit is located. This instrument makes 

 it possible to read temperature to within 0.1 de- 

 gree centigrade and to know the depth of the sens- 

 ing unit to within plus-or-minus 0.5 centimeter. 

 It is intended to be used at sea from a skiff or 

 tender rather than from the research vessel itself. 

 (30) 



THERMO PHILE . See STENOHALINE. 



THEVENIN'S THEOREM . Thevenin's theorem states 

 that, if an impedance be connected between any two 

 points of a circuit the resulting steady-state cur- 

 rent through that impedance will be such that its 

 phasor is the quotient obtained by dividing (1) the 

 phasor of the potential difference between the two 

 points prior to the connection by (2) the sum of 

 the phasors of the connected impedance and the 

 impedance of the circuit measured between the two 

 points prior to the connection. (4) 



THIXOTROPHY . The property of a material that 

 enables it to stiffen in a short time upon stand- 

 ing but upon agitation to change to a very soft 

 consistency or to a fluid of high viscosity. The 

 process is completely reversible. 



TIDAL CURRENTS . See APOGEAN TIDES. 



TIDAL FIAT . A flat, soggy area which emerges dur- 

 ing low tide, that is characterised by the simul- 

 taneous deposition of clay and sand by tidal waters. 

 (15) 



TIDAL INLET (TIDAL OUTLET) . 1. A natural inlet 

 maintained by tidal flows. 



2. Loosely any inlet 

 in which the tide ebbs and flows. (11) 



TIDAL OUTLET . See TIDAL INLET. 



TIDAL PLATFORM ICE FOOT . An ice foot between high 

 and low water levels, produced by the rise and fall 

 of the tide. (17) 



TIDAL PRISM . The total amount of water that flows 

 into the harbor or out again with movement of the 

 tide, excluding any fresh water flow. (11) 



• 

 TIDAL STREAM . In British usage the expression is 

 applied to a tidal current, their use of the word 

 "current" being confined exclusively to the non- 

 tidal horizontal flow of water. (14) 



TIDAL VOLUME . In physiology - the volume of air 

 moved in and out during a single normal respira- 

 tory cycle. During rest, the tidal volume general- 

 ly averages about one-half liter. Tidal volume 

 increases considerably during physical exertion. 

 It naturally cannot exceed the vital capacity. (37) 



TIDE. The periodic rising and falling of the water 

 that results from the gravitational attraction of 

 the moon and sun acting upon the rotating earth. 

 Although the accompanying horizontal movement of 

 the water resulting from the same cause is also 

 sometimes called the tide, it is preferable to 

 designate the latter as TIDAL CURRENT, reserving 

 the name tide for the vertical movement. (14) 



TIDE GAGES . Devices used to measure the rise and 

 fall of the tide. They may be divided into two 

 classes; nonregistering gages which require the 

 observer to record the heights of the tide and self 

 registering or recording gages which are equipped 

 to automatically plot the rise and fall of the tide. 

 Nearly all the tide gages of which there are 



several designs are operated in the U. S. by the 

 U. S. Coast and Geodetic Survey. See also BOX 

 GAGE, PRESSURE GAGE, TAPE GAGE and TIDE STAFF. 

 (35) 



TIDE INDICATOR . A form of tide gage designed for 

 the purpose of clearly indicating on a suitable 

 scale the height of the tide at any time as refer- 

 red to the plane of reference. Such an indicator 

 may be located in the immediate vicinity of the 

 tidal water or at a distance with electrical con- 

 nection. (14) 



TIDE- PREDICTING MACHINE . An instrument that pre- 

 dicts the tide by mechanically summing the harmonic 

 constituents of which it is composed. The tide- 

 predicting machine used by the Coast and Geodetic 

 Survey in the preparation of its annual Tide Tables 

 is described in detail in Coast and Geodetic Survey 

 Special Publication No. 98, "Manual of Harmonic 

 Analysis and Prediction of Tides". (14) 



TIDE RACE . A very rapid tidal current in a narrow 

 channel or passage. (15) 



TIDE RIPS . A turbulent water body produced by op- 

 position to tidal currents. (See RIP CURRENTS) (15) 



TIDE STAFF . A tide gage consisting of a vertical 

 graduated staff from which the height of the tide 

 can be read directly. It is called a fixed staff 

 when it is secured in place so that it cannot be 

 easily removed. A portable staff is one that is 

 designed for removal from the water when not in 

 use. For such a staff a fixed support is provided, 

 and the staff itself has a metal stop secured to 

 the back so that it will always have the same ele- 

 vation when installed for use. (14) 



TIDEWATER . Water affected by tides or sometimes 

 that part of it which covers the tideland. The 

 term is sometimes used broadly to designate the 

 seaboard. (17) 



TIDE WAVE . The ridge of water raised by tidal 

 action, resulting in tides at various places around 

 the world. Also called tidal wave. (17) 



TILLITE . An ancient consolidated till or boulder 

 clay, deposited directly from a GLACIER or an ICE- 

 SHEET. It is an unsorted deposit, often contain- 

 ing striated stones set in a clay matrix. (27) 



TINRO. Pacific Research Institute of Fisheries 

 and Oceanography (USSR) . 



TOMBOLO . An area of unconsolidated material, de- 

 posited by wave action or currents, that connects 

 a rock or island, etc., to the mainland or to a- 

 nother island. (11) 



TONGUE . A projection of FLOATING ICE caused by 

 wind and current. The extent of a tongue may be 

 several miles. (25) 



TOPMARK BUOY . A buoy with a topmark, or character- 

 istic shape secured at the top to aid in its iden- 

 tification. (17) 



TOPOGRAPHY . The general configuration of the land 

 surface (or the ocean bottom); the sum total of the 

 results of erosion and deposition on the physio- 

 graphic features of a region. (27) 



TOROID CONDUCTIVITY CELL . The toroid conductivity 

 cell is a device used to measure the electrical 

 conductivity of sea water by relating a signal vol- 

 tage to the resistance of the electrical path in 

 the water. (35) 



TOTAL ICE SEASON. MAXIMUM . The longest ice season 

 recorded over a period of years in an area. See 

 ICE PERIOD. 



120 



