Chap. VIII.
BRITAIN.
443
built was, by Mr. Mylne’s measurements, “ 19,586 feet superficial nearly, taking the widthequal to the length of the bridge, and the depth from the face of its bed, underneath thearches, up to the visible marks of the flow of the tide on the modern stone-work. It isreasonable to suppose, the bridge being removed, that would be the space through whichthe tidal waters would flow. The water-way of all the arches or locks added together,taken from the surface of the starlings (which are 1 foot 10 inches out of a level endways,and not altogether on a level with one another across the river) down to the floors of thelocks respectively, was, in 1767, 3530 feet superficial. The water-way of all the said archesabove the starlings to high water mark, above mentioned, deducting the triangular spaces atthe haunches of each arch, forms a space of 4470 feet superficial. Now, these added toge-ther form the whole space of 8005 feet nearly, and this is very much diminished in itspowers by being divided into nineteen parts, one very large, and many others exceedinglysmall. It is further diminished in its effects by stages and piles, stretching 290 feet alongthe bridge ; and by as much as the water-wheels at their periphery do not move so fast asthe current of the stream in the face arches, and thereby producing a considerable retard-ation of the due effect there would be if they were not there. Many of the floors of thelocks have been raised to a degree of no small danger, and the outsides of the starling havebeen covered with planking since 1767, all of which last make considerable deductions fromthe quantity of 8005 feet; yet if that space alone be deducted out of the area of the whole,there remains of solids in this bridge 11,581 feet superficial. This is nearly a proportionof the solid parts, occupying three-fifths of the river, and leaving only two-fifths for thepassage of the whole river.”
The water-way at Westminster Bridge was, before it was built, 19,010 feet superficial,and now 14,768 feet, so that the piers occupy 4242 feet superficial only.
The water-way at Blackfriars was, between the present shores before the bridge was built,19,083 feet superficial ; the water-way of all the arches or openings is 15,081 feet super-ficial, and the piers occupy a space of 4001 feet superficial. The proportions then are asfollows : —
Area of Kiver.
- 19,586
- 19,010
- 19,083
Solid.
11,581
4,242
4,001
Water-way.
8,005
14,768
15,082
When the committee of the House of Commons had determined upon the erection of anew bridge, Mr. George Rennie, at the desire of his father the late Mr. Rennie, made thedesign as it is now executed; and as the country lost the services of Mr. Rennie by his deathin 1821, the execution of this important undertaking devolved upon his sons, and Mr.George Rennie holding at that time a situation under the government, his brother Sir John,who was his junior, was named the acting engineer. Messrs. Joliffe and Banks were thecontractors, and the cost, including the approaches, amounted to £1,458,311 8s. ll^rf.The first pile for the cofferdam was driven on the 15th of March, 1824, and the dam wasfinally closed on the 1st of April the following year, and after the water had been pumpedout 29 feet below low water mark, it was found remarkably tight.
On the 27th of April the workmen commenced their excavations in a stiff blue clay,after which the sills and planking were laid ready for the foundations, which were com-menced on the 15th of June : the first stone laid was a piece of Aberdeen granite, 5 feet| of an inch long, 3 feet 6^ inches broad, and 2 feet 10 inches deep, containing 50 feet7 inches cube, and weighing 4 tons.
The cofferdam for the second pier was completed soon after, and pumped out by the24th of August; in 1826 the foundations on the Southwark side, comprising the abutmentand wing-walls, were carried up, and the second pier was commenced.
The coffer-dams of the first and second piers being no longer required, a portion of thepiles were cut off on both sides, to prepare them for the support of the centres; and afterthe horizontal wedges were fixed on the heads of the coffer-dam piles, on the 30th Septemberthe first rib was set up by means of large sheer poles and powerful hoisting tackle, andby the 10th November, the whole ten ribs were placed.
When the masonry of the second pier was sufficiently advanced, the centre, which hadbeen framed in the Isle of Dogs, was floated up the river, and being hoisted upon a largedouble barge, was raised into its place by means of screws, assisted by the tide. Thecofferdam of the third pier had by this time advanced, and soon afterwards that of thefourth pier, when it became necessary to provide more water-way by removing the pierbetween the fifth and sixth locks of the old bridge, and forming a wooden tressel frame ofwhole timbers for the traffic to pass. This was performed at the cost of 8000Z. by demo-lishing one half of the arch at a time, after which the pier below was taken away 4 feetbelow low water mark. By the 4th of August, 1827, the first arch was completed ; by theend of the year the second arch was keyed in, the foundation of the third pier completed,and that of the fourth laid. In 1828, the water being pumped out of the north abutmentdam, and the excavations made, the first pile was driven on the 1st of February, and the