109 



isobaric weather map. The dynamic topographical map (fig. 49) 

 is read also in the same manner as one reads a meteorological map. 

 The oceanic situation around the Tail of the Grand Bank April 29 

 to May 5 may be described as follows: A "low" or hollow in the sea 

 surface lay centered off the southwest slope of the Grand Bank with 

 a trough, circumscribed by the contour of 728.70 dynamic meters, 

 extended around the Tail to the northeastward more or less parallel- 

 ing the 100-fathom curve. The sea surface was relatively high in over 

 the Bank itself and at the outermost stations offshore. A liill of water, 

 figuratively, lay centered about 65 miles southeastward of the Tail. 



Fig. 49.— Set I. Dynamic topographical map 



The circulation of the water, which will follow this dynamic topog- 

 raphy of the surfaces is in general as on a weather map, anticlock- 

 wise around the "lows" and clockwise around the "highs." Figure 

 50, page 110, indicates the direction of flow of the water by means of 

 the arrows, and the numerals represent in knots per horn* the veloc- 

 ity of the current at the particular place and time. The velocities 

 were calculated upon the assumption that the water had no motion 

 at a depth of 750 decibars (meters). Such, however, was not liter- 

 ally the case, especially offshore in the Gulf Stream, but inasmuch as 

 750 decibars was the limit of depth to which our observations ex- 

 tended, it is taken arbitrarily as the depth at which motion most 

 nearly approached zero. Reference to Figure 50, page 110, shows 



