the Foundations of Bridges, &c. 411 



Tt has been very improperly stated, that starlings are ne- 

 cessary to defend the piers when coiisiructed after the man- 

 ner kst described : on the conlrarv, the use of starlings is 

 not to defend piers of any particular construction ; they 

 have been used generally, when, by the plan of the bridge^ 

 too little waterway has heen left; and are a very defective, 

 extravagant and absurd remedy* tending to increase the evil 

 the effects of which they are meant to oppose. The fol- 

 lowing tabic exhibits the proportion of the waterways at 



the three bridges in London. 



Area of the River. Solids. Waterway 



London Bridge . . . 

 Westminster ditto 

 Blackfriars . . ditto 



19,586 il,38i 8,003 



19,010 4,242 14,768 



19,083 4,001 15,082 



Hence it appears that three-fifths of the water at London 

 bridge is dammed up: the consequence has been, that the 

 river at this part, by the increased velocity of the water, has 

 had increased action on the bed, and ii has been deepened 

 14 feet below its general surface, and the piers have been 

 and are always sTibject to be undermined; while at the 

 other bridges, where the waterway is duly proportioned to 

 the quantity of the water, the bed of the river has remained 

 stationarv, and starlings or any other expedient have not 

 been necessary to protect their piers. 



It is manifest, upon whatever principle of construction 

 the piers of London bridge might have been built, with 

 the same proportion of solids to waterway, starlings, or 

 some other meins having a similar effect, must have been 

 resorted to ; and it may be inferred that, had the same pro- 

 portion of waterway to solids been preserved, as in the 

 other two bridges in London, there would have been in- 

 herent in it the same probability of duration ; nor would 

 there 'have been any more occasion to have recourse to 

 starlings* 



The method practised by the builders in the middle ages 

 has got into great disrepute, from the prejudice in those 

 times in favour of arcs of circles for the forms of their 

 arches ; and they were unable, or wanted courage, to erect 

 arches of a great span, with a small versed sme : where 

 the heights of the banks of rivers have permitted them to 

 use an are of a circle with an elevated versed sine lor the 

 form of the arch, they have exceeded both the ancients and 

 moderns in the length of the chord. 



The piers of their bridges were generally numerous, and 

 their arches small, rendering an easy ascent to the passen- 

 ger : an oyer anxiety for security induced them to make 

 D d 2 eacti. 



