249 



Where A is the coefficient of eddy diffusivity, Tq and r, 

 are the radii of the initial and final areas, /s''^^ 2,5, and 

 Tq and T, are the times at the beginning and end of travel. 

 Ifr=0, To=0, and \ = 2.5, then: 

 A = r^ / 12.5 T, 



In using this formula as a first approximation to A, 

 rj was taken as one-half the length of shore line along \Ndiich 

 recoveries were made, neglecting those cards which drifted 

 for vinreasonably long times or long distances. This involved 

 some judgement as to the distance r. beyond which there was 

 no concentration, and it also required that the mass of cards 

 approach the beach at not too small an angle. Whenever the 

 group of cards approached the shore at a more acute angle, 

 a simple method was devised by which both r, and T, could be 

 estimated, but there was no opportunity to extend the work 

 to include such stations. If the time or distance of drift 

 is long, and only a portion of the cards diffused far enough 

 to reach the shore, the method developed by McEwen for such 

 a case can be used. 



Values computed for the coefficient of eddy diffusivity 

 for individual stations ranged from 1„2 x 10 to 6,1 x 10 

 cm '^ /sec. However, most values lay between 4 x 10 and 3 x 10 , 

 and the mean value was 1.27 x 10 cm /sec. This result is 

 entirely consistent with those obtained by other investigators 

 and by other methods which are summarized by Pearson (1955). 



The times of drift varied from 2 to 16 days. The average 

 distances travelled between points of release and the shore 

 were 8 to 13 miles. 



