230 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[July, 



the masonry all of bi-lon, (the backing of the arch and 

 abutments keeping pace,) until reaching the height fixed. 

 The exterior faces of the abutments, (not next the earth,) 

 and of the walls, were formed by some planks stronglv 

 fixed, against which the bi'ton rested. These planks 

 were removed, two or three days after, and the faces of 

 beton remained exposed, and were very well preserved. 

 At the height of the springing of the arch, we laid five 

 courses of bricks plumb on the faces of the abutments, to 

 serve as perpendicular faces for the centre to fit up 

 against, and enable it to detach itself easily. 



Fifteen days after the laying of the last bi-ton, we 

 commenced the construction of the centre, composed of 

 many courses of bricks, laid flat, in succession, (from 

 the springing towards the crown,) following the curve of 

 the arch at the intrados, built partly with plaster, and 

 partly with cement, or hydraulic mortar, and supported 

 at the springing by projecting masonry, or bv a timber 

 for that purpose. Thecentre was formed of four ourses 

 of bricks (in thickness, or depth, say nine inches) ; the 

 three lower were laid with plaster, and the upper course 

 with cement, to shelter the plaster from the dampness 

 of the bi'lon. The upper bricks of the centre were 

 covered by a bed of mortar or clay, in order to model 

 perfectly the intrados of the arch, and to hinder the 

 bi'ton from forming one body with the bricks. 



The construction of the centre being finished on the 

 17th of August, we established, three davs after, the 

 masonry of the two heads of the arch of brick, (in lieu 

 of quoin stone,) which were completed ou the 2(ith of 

 the same month. 



Immediately after the construction of the two heads, 

 we wrought them into the general mass of beton, forming 

 the arch ; this operation wis finished on the 5th of Sep- 

 tember, with the exception of the backiug up, which 

 was accomplished, on both sides, the 11th of the same 

 month. The beton of the arch was composed in the 

 same manner as those of the abutments, and manipulated 

 by the same process ; hut we added to it 2-ji, cubic feet 

 of cement for every 3.14 cubic feet, or T yth of the mass, 

 to augment the strength of the mortars of the • 

 the arch. This construction was made without following 

 any regular order, and the bHon was cast in mass :s, 

 upon the centre, to the thickness of two feet, which formed the first 

 general bed, or layer, on the development of the arch. This first 

 bed being finished, we formed the second in order to reach the thick- 

 ness of three feet at the key, the spandrel backing, and the abutments 

 being levelled up. A coping of hydraulic mortar was then placed 

 over the whole extent of the arch, and covered immediately with a 

 layer of clay, strongly beaten. 



All was left in this" state until the 25th of January, 1841; we then 

 proceeded to the operation of the striking of the centre of the arch. The 

 28th of January, the centre of bricks was taken away, and the intrados 

 of the arch appeared very even in all its parts. After three months, 

 it manifested not the smallest settlement in its masonry, and, since 

 then, the bridge has stood through the summer, without incurring the 

 least degradation capable of affecting its solidity. This bridge has a 

 clear opening of 39j feet between the abutments ; the middle is placed 

 in the axis of the canal, which has two towing paths ; its breadth is 



Fig. 1 



- KB - 



Explanation OF THE Figures. 



a, canal; b. abutment of beton; r. mass i f of beton; dil, towing paths; 



c ijuoin^ of bridge upon the towing-paths, built ol hrge stone, with the ang'c, rounded ; 

 /". arrises of the soffit, or quoins of luck r.t each be.ul of the arch, instead of the usual 

 ■ one. 



193 fe 't between the he ids, or faces, of the rings ; and the arch is 

 formed of a segment of a circle of 39i feet chord, and 51 feet rise, 

 or versed sine. 



The entire mass of the abutments is of bi'ton, except the four angles 

 on the sides of the towing paths, which are of large stone, rounded on 

 the arris, on account of the rubbing of the towing lines. The arch is 

 also of bHon, as are the faces of the tympans, or spandrels, and the 

 intrados with the exception of the arrises of the solvit, or quoin of the 

 heads, which are of brick. 



M. Lebrun has joined to his memoir, along with a plan of the 

 bridge of (irisoles, manv certificates, from the mayor of this commune, 

 and from the engineer of the lateral canal of the Garonne, proving the 

 complete success of the works, and the solidity of the construction, 

 which has endured the proof of the passage of loaded carriages, the 

 numerous influences of heat, and some very severe frosts, without 

 having suffered the least degradation. 



OLD LONDON WALL. 



A Letter from Mr.. George Godwin, KR.S., &c. 



"Some there are who cry down tl u i.h much con- 



tempt, as too curious a search after what is pas; ; « hose authority as 1 shall 

 not altogether slight, so 1 shall not much regard their n Igment. 



Cam 



On the west side of a vacant plot of ground in George Street, 

 Tower Hill, and behind the houses in Trinity Square, stands one of the 

 most considerable remaining portions of the wall which was anciently 

 built tor the protection of Londinium, (probably at the commence- 

 ment of the fourth century,) and which for some'time was considered 

 ot the utmost importance, and kept constantly repaired. As, however, 

 the number and power of the citizens increased, they outgrew their 

 shell, (it wis but ., small one,) and the irruptions of barbariaus ceasing 

 to be frequent, this protection was considered of less and less conse- 

 quence; until at List, as Camden observes, the Londoners slighted 

 tenceci cities, as tit for nothing but women to live in, and looked upon 



I their own to be safe, not by the assistance of stones, but the courage 

 I of its inhabitants. Year after year has witnessed the gradual de- 

 struction of the remains of this "ancient enclosure, until, with the ex- 

 ception of a bastion in Cripplegate Church-yard, the portion behind 

 < Trinity Square, of which I am ..bout to speak, a continuation of it 

 , forming the back wall of Mr. Atkinsou's hemp warehoi.se in Cooper's 

 i Row, and a few inconsiderable fragments to be found in the str»et to 

 which it gives its name, it has been entirely swept away. ' 



The portion in question is also now threatened with destruction ; 

 and the object of this communication is in aid of other efforts which 

 have been made, to induce those who have authority to re-consider 

 the matter, with the view of avoiding this objectionable step if pos- 

 1 sible. It is intended to build a church on the vacant ground in 

 George Street, with the special object of affording accommodation 

 to the masters, officers, and seamen of the ships in the docks and the 

 ; river; and it is considered that the site of the old wall " is essential 



' For interesting pal I •"'> eVi'ion of 



Stow's "S bap. II, p. 7. Also 1 • • I 1 180. 



