FETCH, EXPOSURE, AND WAVE-POWER. 75 



For instance, the worst sea that is experienced at the harbour 

 of Holyhead is caused by a north-west gale veering to north. 



Similarly at Scrabster, on the north coast of Scotland, which 

 lies under the shelter of Holburn Head, a north-west or north- 

 north-west gale veering to the north or east of north causes the 

 waves to wheel round the headland, and sends the heaviest sea 

 into the bay. Again at Alderney, the worst seas are caused by 

 south-westerly gales veering to north of west. At Algoa Bay 

 (Cape Colony), very heavy rollers wheel round Cape Recife. 

 These are caused by south-west gales, which, unless a compre- 

 hensive view of the district were taken, would be looked upon 

 as blowing off shore. These rollers are sometimes so heavy that 

 they prove more trying to the sea-works at Port Elizabeth than 

 higher waves set up by gales blowing directly into the bay. 



Were it necessary, numerous other examples might be given 

 to illustrate this wheeling of waves ; but those already cited will 

 no doubt be considered sufficient. 



In connection with depth of water, as affecting exposure, I 

 may here mention a condition which is liable to be overlooked. 



In judging of exposure from a chart or plan giving soundings, 

 it is essential that the nature of the sea-bed, and its liability to 

 scour or not, be ascertained, because the depth of water in front 

 of some sea- works is often much increased by scour during the 

 early stages of a gale. Heavier waves are thus enabled to 

 advance further and further inshore during the continuance of 

 the gale, and to throw their full weight against any opposing 

 work. At Port Elizabeth I have often noticed such a deepening 

 take place to the extent of 5 or 6 feet in a single tide along the 

 front of the sea-wall there ; and on the coast of Holland, in the 

 neighbourhood of Ymuiden harbour, the water frequently 

 deepens to the extent of fully 10 feet during the early part of a 

 gale. When it is remembered that every extra foot in depth 

 may mean an additional foot in height to the waves assailing a 

 work, the significance of this scouring action will be appreciated. 



Wave-Power. On many coasts there are such astounding 

 exhibitions of the apparently herculean power of waves, that we 

 are led to consider whether the waves may not have been aided 

 in the part they played by some power or circumstance of which 

 we are not now cognizant, but which may have rendered the 

 display of such seemingly prodigious force unnecessary in bring- 

 ing about results such as those to which I now refer. 



