Chap. VIII.

BRITAIN.

427

figure is supported, it must be because in its thickness some catenary was included;”notwithstanding, no attempt was yet made to introduce its form into the arches of bridges,nor had the cathedral vaulting been sufficiently noticed by our engineers.

Blackfriars Bridge .— During the time that the improvements ofLondon Bridge were carrying on, the Common Council undertook toopen a new and magnificent entrance into the centre of the metropolis,by a stone bridge at Blackfriars. After discussing this project forseveral years, it was at last referred to a particular committee, anda report was made in answer thereto, in September, 1754; this wasfollowed by a design, made by Mr. Dance, the surveyor to the cityworks, the estimate for which was £185,950, exclusive of purchases ofproperty, and if the foundations for the bridge required piling, the costwould be increased.

The City afterwards applied to parliament, and obtained an act toerect a bridge, with a grant of a reversionary toll, and a power toborrow £160,000 upon the credit thereof. This act was passed in theyear 1756, and two years afterwards, twelve aldermen and twenty-fourcommoners were appointed to carry the same into effect. Designswere afterwards advertised for, and on the 4th of October, 1759,many drawings and models were received by the committee ; objectionswere made to the form of the arches in the design presented by Mr.

Robert Mylne , as deficient in strength and stability, which objectionswere ordered to be laid before eight gentlemen of the most approvedknowledge in building, geometry, and mechanics, for their opinion andadvice. In February, 1760, their opinions were delivered in, and itwas then determined that Mr. Robert Mylne ’s design should beadopted.

The proceedings of the commissioners for Westminster bridge werethen consulted, and the committee advertised for proposals, which wereto be accompanied with a specification of different prices for peace andwar, a caution never before practised, but by which a saving was madeof £5,839.

After the proposal had been received, and all duly examined, themasons’ work was given to Mr. Joseph Dixon, the carpenters’ work toMr. John Spencer, the smiths’ work to Mr. Bryant, and the ballastwork to Mr. Cox and three others.

In forming the contracts particular care was taken not to admit adoubt, about either the manner of execution or payment; explicit ruleswere laid down for the admeasurement of every species of work; thefirst stone .was laid on the 31st day of October, 1760.

A careful examination was made by boring for the foundation ofevery pier, and the piling was in proportion to the respective texturesand solidities, the architect having convinced the committee of thepracticability of driving piles under water, and of cutting % them levelwith the bed of the foundations, by an invention of his own.

In fixing the position of the bridge, it was desirable that two objectsshould be obtained; one, that its direction across the river should beat right angles with the streams of ebb and flood, the other, that itssituation, with regard to the bed of the river, should fully answer thepurpose of navigation. The great inequality in the bed of the river,where the depth of stream was thrown towards the Surrey shore,made it expedient to place the great arch nearer the latter than theformer, as otherwise most of the arches on the London side would at lowwater have stood upon dry ground, and a great part of the bridgewould have been rendered useless to the navigation, and in consequenceof this position being taken, the northern abutments were extended to agreater length than the southern.

As soon as a part of the bridge was passable, a temporary arrange-ment was added, by which the public were enabled to cross, and thetoll received was added to the building fund.'

In December, 1770, the surveyor applied by a memorial, as thebridge was nearly finished, for the monies due to him to be settled andpaid ; and the committee, after several days’ consideration, determinedthat he was entitled to receive a commission of five per cent, on worksdone, of one per cent, on purchases made, being the same as allowed atLondon Bridge .

Fig. 431,