236 WAVES OF THE SEA 



all that was noticeable from the front. But when 

 the bore came opposite to me, the water being 

 deeper below the part of the bank on which I 

 stood, the steep, bold front was gone in an instant ; 

 a rounded wave or swell, followed by others of 

 the like size and form, being immediately sub- 

 stituted, and the number of these swells rapidly 

 increased, the group lengthening to leeward, so 

 that in a few seconds I counted no less than sixteen 

 of these large swells, 1 forming a group of waves 

 of remarkable appearance, which progressed, as 

 a whole, with singular slowness, owing, I suppose, 

 to the well-known circumstance that the speed of 

 a group of waves (at least in deep water) is only 

 half that of the individual wave. The above obser- 

 vation suggests important reflections upon the 

 nature of the tidal bore. This term is by common 

 consent employed to designate a steep-fronted 

 wave, either overf ailing or on the verge of break- 

 ing, constituting the first rise of the tide in ia 

 river or estuary. If it be actually a part of the 



1 These are often referred to as " ripples," but the etymology 

 of the word indicates the propriety of restricting its use to little 

 waves. Its use for waves of capillary size, as proposed by Lord 

 Kelvin, may be conveniently extended in the case of other 

 materials e.g., sand and snow to a small class of waves only 

 affecting superficial strata, co-existing with larger waves capable 

 of indefinitely great development. 



