AND OTHER WATER WAVES 93 



On September 1 6, 1900, in fine weather at 

 Branksome Chine, I heard the boom of surf, and, 

 looking from my window, timed a set of well- 

 formed though not large breakers at the following 

 intervals, viz. : 



18, 17, 19, 23, 19, 21, average 19*5 seconds. 



The following observation of a swell from the 

 Atlantic was made on the north coast of Ireland, 

 near the Giant's Causeway, in the autumn of 1870, 

 by the late Sir G. G. Stokes. 1 One morning a 

 grand surf came rolling in. There had been, some 

 days before, a long succession of heavy gales in 

 the North Atlantic. The period determined from 

 different sets of six or eight waves was 1 7 seconds . 

 The average difference between the mean periods 

 of the different sets of waves was only about i-sth 

 of a second. The differences between the periods 

 of individual waves is not recorded, but would, of 

 course, be much greater. Somewhat later the 

 period sank to 16 seconds, in the latish afternoon 

 to 1 4, and next day to 13. The surf was highest 

 for the 1 7 -second period. During several other 

 summers, when Sir G. G. Stokes spent a month 

 or two on that coast, he never saw anything so 

 striking . 



1 Discussion in Section A, British Association, Dover, 1899, 

 on a paper by the present author. 



