AND OTHER WATER WAVES 125 



hour * ( length 3 7 1 feet ) should enjoy special 

 opportunities for development in depressions where 

 the wind exceeds that velocity. 



We see, therefore, that waves of 68-78 statute 

 miles per hour, which are the greatest speeds I 

 have recorded for swells after Atlantic storms, 

 would in almost all cases outrun them, even when 

 the depression advances along a straight path. 

 The reason that such waves are not developed to 

 greater heights is, therefore, not only that the wind 

 is, during most of the time, not strong enough, 

 but also that the cyclones advance too slowly. 



The above method of theoretical treatment is 

 of only occasional application on account of the 

 fact that there are generally several neighbouring 

 cyclonic systems on the North Atlantic and that 

 the actual winds are a compromise between them. 

 Fortunately, the charts for December 27, 28, and 

 29, 1898, enable us to examine an instance of 

 this commoner condition. A series of cyclonic 

 systems were following one another across the 

 North Atlantic from S. of W. to N. of E., and 

 strong westerly winds prevailed during the whole 

 of these three days between N. 50, W. 40, and 



1 This is a wave of a little more than 8 seconds period. The 

 8-seconds wave has a speed of about 28 statute miles per hour 

 and a length of 328 feet. 



8 



