Generation, Growth and Propagation of Waves 



103 



wave-train is the remainder of a itrong swell which developed on the southern 

 side of a cyclone which moved towards the British Isles, thereby decreasing 

 in force. Simultaneous! v the force of the swell decreased. 



Fig. 45. Swell in North Atlantic 15 November 1938, 12h G.M.T. (Keyser). 



Particularly interesting is the study of the propagation of a strong swell 

 which started at the end of February 1 886 from a storm area south of New- 

 foundland (40°N., 55°W.) and which could be followed, according to the 

 ships logs, right across the subtropical and tropical Atlantic Ocean to the 

 coast of Ascension Island (March 1886). This study allows some insight 

 into the behaviour of swells during such a long travel over large oceanic 

 areas. The main results have been summarized in Table 14. Seven reliable 

 time measurements, recorded in the ships logs, permitted to follow a part- 

 icularly high wave-train in its progress through the trade-wind region. The 

 distances have been measured from the assumed centre of the hurricane 

 (on 25th February) in 40°N., 55°W. along the great circle. Even though 

 the time of the start for determining the "age of the swell" is undertain, the 

 time differences between the observations of the individual ships are probably 

 dependable. The velocity computed from these observations is approximately 

 30 n.m.per hour at the start, increasing then to 41 A, and off Ascension it was 



