at intervals of 27 feet, to the temperature sensors, or thermistor 

 beads. 



The upper ends of the electrical leads are connected to a 

 recorder located in the ship's laboratory. Signals from the leads 

 are scanned electronically every 10 to 12 seconds, and lines shovi^- 

 ing the depths of isotherms are printed on IQ-inch-vi'ide tape. 

 This procedure is equivalent to lowering a bathythermograph 

 every 100 to 120 feet at a ship's speed of 6 knots. Also printed on 

 the same tape are the depth of the fish at the end of the chain, 

 which is the maximum depth of observation, and the temperature 

 of the sea surface. 



With the thermistor chain it is possible for USS MARYS- 

 VILLE to lower a string of temperature sensors into the water and 

 then cruise ahead with the string suspended vertically from its 

 fantail. Since elements are sensing from the surface down to about 

 800 feet while the ship is moving through the water horizontally, 

 two dimensions of coverage, depth and distance, are achieved. , 

 However, time, a third dimension, must also be considered. 



The thermal structure presented here is more properly the 

 "structure of encounter, " or "depth of encovmter, " of isotherms. 

 The vertical scale is depth, but the horizontal scale may be con- 

 sidered as both time and distance. The amplitude of the vertical 

 changes in isotherms is correct in either sense, but in 10 or 12 

 hours some time changes must certainly have occurred at the be- 

 ginning of the section when the end is being recorded. The struc- 

 tures will in reality portray a spatial plot rather than time changes 

 since the advective and vertical-oscillation changes caused by in- 

 ternal waves occur much more slowly than the movement of the 

 ship across the section. Therefore the detailed thermal-structure 

 data presented (fig. 3) can be described as vertical sections in the 

 sea in the same manner as are other oceanographic sections de- 

 rived from serial station data. 



