92 WAVES OF THE SEA 



was calm, after some days of light winds from 

 north and east. A heavy swell began to come in 

 upon the shore at about n a.m., and between 

 3 and 4 p.m. I timed the arrival of twelve succes- 

 sive breakers, between which the eleven intervals 

 were as follows : 



23, 23, 22, 22, 22, 23, 21, 24, 24, 22, 22, average 22-5 seconds. 



This is the longest period which I have ever 

 observed for a group of waves. It was noted at 

 the time as a good observation i.e., the determina- 

 tion of the times was rendered easy by the regu- 

 larity in the form and progress of the waves. 

 Multiplying the period by three, we obtain with 

 sufficient accuracy the speed in deep water, ex- 

 pressed in knots, which is therefore 67.5. This 

 multiplied by 7-6 gives the speed in statute 

 miles per hour, viz., 78.75. The corresponding 

 wave-length in deep water is 2,594 feet. Although 

 observed in the English Channel, it is an accepted 

 view that such a swell is due to an Atlantic storm. 

 The period is almost twice as great as that (11.7 

 seconds) recorded by Dr. Scoresby in the storm of 

 March 5-6, 1848, and the speed therefore is like- 

 wise nearly twice as great. In a later chapter 

 an account will be given of the probable origin of 

 this set of breakers and of the distances they had 



travelled ( see p . 1 1 8 ) . 



