FOR GREA T BRITAIN AND IRELAND. 69 



confine his attention to the local depth which exists imme- 

 diately in front of the harbour, but to bear in mind the 

 general depth of the sea or ocean on the shores of which his 

 work is to be placed." 



" If, however, the shoal water immediately in front of a 

 harbour extends seawards for a considerable distance, so as 

 to form an extensive flat beach or foreshore, that depth does 

 become the true limit for the maximum wave, whatever may 

 be the general depth of the sea outside. The small depth 

 over the outlying rocks at Arbroath, Mr. Leslie found, had 

 the effect of tripping up the heaviest seas, and thus destroy- 

 ing them before they reached the harbour, while it was still 

 sufficient to allow the smaller waves to pass over the shoals 

 and reach the works in an unbroken state. It thus appears 

 that the largest waves are not always so destructive as 

 smaller waves. We may also conclude that in some cases 

 of severe exposure, where it would not interfere with the 

 passage of ships, the waves might to some extent be re- 

 duced by dropping very large stones at some distance 

 seaward of the works, so as, by forming an artificial shoal, to 

 cause the waves to crest and break outside. On the other 

 hand, it is quite possible that there maybe a very consider- 

 able depth at low water close to the pier, arising from the 

 geological formation, or due -to the scouring action of a 

 local current, while the general character of the sea out- 

 side may be that of a shallow basin, encumbered with 

 reefs or sandbanks which render the formation of heavy 

 billows altogether impossible." 



MR. RUSSELL'S LAW OF BREAKING WAVES. 



lk It is of great importance," says Mr. Stevenson, " to be 

 able in all cases to ascertain the maximum possible wave 



