70 IMPROVED FISHERY HARBOUR ACCOMMODATION 



that can exist unbroken in any given depth of water. 

 Mr. Scott Russell, whose observations on what may be called 

 the marine branch of hydrodynamics are of such great value, 

 has stated that * he has never noticed a wave so much as 

 10 ft. high in 10 ft. water, nor so much as 20 ft. high 

 in 20 ft. water, nor 30 ft. high in 5 fathoms water ; but he 

 has seen waves approach very nearly to those limits.' 



"It is presumed that the datum here referred to is the 

 mean level of the surface of the sea." 



" I have had no opportunities of verifying these observa- 

 tions on high waves ; but as the subject is very important, 

 because the depth of water for some distance in front of 

 the work may be said to be the ruling element which 

 determines the amount of force which it has to resist, 

 whatever be the line of exposure, I will simply mention 

 the most satisfactory results that I have as yet obtained 

 on this subject, and which, so far as they go, confirm Mr. 

 Russell's law." 



OBSERVATIONS ON BREAKING WAVES. 



"It must, however, be borne in mind that these observa- 

 tions, and I conceive also those of Mr. Russell, apply only 

 to those short, steep, and superficial waves which are due to 

 an existing wind, and not to the ground swells which are 

 almost constantly to be found in the open ocean, which 

 may be the result of former gales, or are the telegraph, 

 as they have been called, of those which are yet to come." 



