208 



RENNIE'S DOCKS AND HARBOURS. 



PART VII. 



but were found even stronger than solid walls con- 

 taining an equal quantity of material, and those at 

 Grimsby have stood firm until the present day. The 

 contrivance was thought so valuable, that some years 

 after Mr. Rennie had invented it, Sir Samuel Bentham 

 (in 1811) took out a patent for the plan; but of this 

 Mr. Eennie took no notice, having himself, as we have 

 seen, been the original inventor of the process. Indeed, 

 his attention had long before this time been directed 

 to the best form of walls for resisting the pressure 

 of water; and, as early as the year 1793, we find him 

 recommending the adoption of curved walls, in place of 

 the inclined straight-faced walls with perpendicular back 

 formerly adopted. 1 



Another important harbour on which Mr. Rermie 

 was early employed was that of Holyhead, situated at 

 the point of the island of Anglesea nearest to the Irish 

 capital. Although so conveniently placed for purposes 

 of embarkation, everything had as yet been left to 

 nature, which had only provided plenty of deep water 

 and many bold rocks. But Holyhead had neither pier 

 nor jetty, nor any convenience whatever adapting it for 

 harbour uses. Besides, the place was almost inaccessible 

 from inland by reason of narrow, rugged, and in many 

 places almost precipitous roads. The dangerous ferries 



1 The occasion on which this plan 

 was first recommended was in Mr. 

 Rennie's report (1793) on the Hutchi- 

 son Bridge across the Clyde. That 

 bridge, erected by another engineer, 

 fell down on the removal of the cen- 

 tres, on which Mr. Rennie was sent 

 for, post haste, by the Lord Provost 

 and magistrates of Glasgow to confer 

 with them on the subject; and his 

 advice as to the rebuilding of the 

 bridge on another site was subse- 

 quently adopted. It appeared, from 

 an inspection of the ruined piers, that 

 a breast or quay wall had been built 

 on the south side of the river, and to 

 the west of the bridge, which had not 



been executed according to contract. 

 The report stated : " The above walls 

 should be enlarged in their dimen- 

 sions and altered in their construction ; 

 they ought to be carried at least to 

 the level of the river bed, and made 

 five feet thick at the base next to the 

 bridge, and four feet thick at the top, 

 battering one-fifth of their height in 

 a curvilinear form, the beds of the 

 stones being radiated to the centre of 

 the curve ; as the height lessens, the 

 dimensions of the walls may be dimi- 

 nished in the same proportion, and, 

 if built as above described, I have no 

 doubt of the works being perma- 

 nent," 



