11 



vessels bound for United States ports who deviate from the pre- 

 scribed track inevitably incur, over and above the ordinary hazards 

 of ocean travel, the added peril of unlmown drifting ice shrouded 

 by almost continuous fog, and must lose rather than gain time. 



Figure 2. The observed drift of an iceberg from April 10 to 29 plotted against the stream lines of the current 

 map completed April 11 (fig. 45). Triangle represents the berg, dashed line the berg's drift track, and the 

 arrows the current direction. Figures indicate the date, some omitted for clarity. (See text.) 



A DISCUSSION OF THE FORCES AFFECTING THE MOVEMENT OF 



BERGS 



During the period from about April 1 to the termination of active 

 patrol for the season the oceanographic vessel of the Ice Patrol Force, 

 the General Greene, makes periodic oceanographic surveys of what is 

 considered the critical area (fig. 1). The region covered is varied as 

 seems necessary. From the data collected in these surveys, charts 

 of the surface currents are immediate^ constructed on the General 



147469—40 2 



