Figure 12. Isobars over the North Atlantic on 

 Nov. 7, 1931, at 13?^0 G.M.T. taken from the meteor- 

 ological charts of the Northern Hemisphere . Original 

 observations are omitted, except a number of ships' 

 observations of wind. A generating area and the dis- 

 tance of decay for sv;ell traveling toward northwest 

 Africa are indicated. 



The duration was determined in the following manner: 



On 



November 6 a wind of 20 knots had blown over the generating 

 area and had been preceded by stronger winds . The waves present 

 on November 6, therefore, were the highest possible at that wind 

 velocity, that is, according to Plates II or IV they were 10 feet 

 high. A wind velocity of 29 knots would need 7 to 8 hours to 

 raise these waves (Plate IV) and the duration of the wind, was 

 therefore 32 hours. 



53 



