FOR GREAT BRITAIN AND IRELAND. 113 



the entrance without making, at the same time, a pro- 

 portionate enlargement of the internal area, or providing 

 other works for counteracting the effect. As the depth of 

 the water is more and more increased, waves of greater 

 height become possible at the entrance, so that large v 

 waves gain admission to the interior." 



"At the port of Sunderland, Mr. D. Stevenson recom- 

 mended the removal of nearly the whole of the inner stone 

 pier, and the substitution of works of open frame work, 

 in order to tranquillise the interior. These works, which 

 have been quite successful, were rendered necessary by 

 the frequent dredging of the channel at and near the 

 entrance." 



ADVANTAGES OF Two ENTRANCES TO A HARBOUR. 



On this matter Mr. T. Stevenson instances Peterhead, 

 which has two harbours, the north and south. These were 

 united some years since by a canal, and the advantage has 

 been of the most marked character. Vessels can now clear 

 out by the north or south mouth, according to the state of 

 wind or sea. In making such an arrangement, however, 

 Mr. Stevenson observes that some caution is necessary, as 

 the run is apt to extend from the one harbour to the 

 other, unless there be a considerable area ; and where the 

 tides are strong the currents may also prove troublesome. 



Refuge harbours have constantly two entrances, and are 

 of so great extent that they would often be inconvenient to 

 enter if only one were provided. Cherbourg, Portland, 

 and Plymouth have each two entrances. As these large 

 spaces of water are enclosed anchorages, and not harbours 

 in the limited sense of the term, the objections regarding 

 the run of the ground-swell do not of course apply. 



VOL. IX. E. 4. I 



