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HISTORY OF ENGINEERING.

Book I.

The report made by Mr. Robert Mylne on the state of the Ilivcr Thames and its bed,on the structure of London Bridge , and the navigation of the river above and below it,in the year 1800, contains the principal information on those sulyects furnished to theselect committee.

In this report he states, that whilst the alterations were making at London Bridge in1761 and 1762, and during the removal of the pier under the great arch of 70 feet span,he was consulted by Parsons, the contractor, as to the best manner of performing hiscontract; and he advised that a hole should be made in the ashler works forming one sideof the old pier, on which the two Gothic arches rested, which was to be removed. Onexamination it was found that the pier rested on four rows of piles, driven closely togetherround its outer edge; the tops of which were at a very considerable depth below thepresent low water mark. Around these and forming the starlings were others, which hedrew up by means of powerful screws fastened to the heads, and then, by destroying someof the ashler work, he was enabled to displace and draw some of the outside quadruplerow, on which the foundations of the pier were laid; the pier quickly became a ruin, anddissolved away in the midst of that impetuous agent, the fall under the bridge. The outerpiles being carried away, the heart or middle of the work was borne off so suddenly, ashardly to leave any time to consider and measure its substance and texture. All thatcould float was dispersed up and down the river; but some of the original piles were pre-served, which were stated to have been there about 586 years. The original bed of theriver, under the substance of the pier, had never been exposed to such a rapid streambefore; it was then much higher in level than any parts above as well as below the bridge;its substance was soon worn away by the powerful friction, and in proportion as the spaceand depth were enlarged, the violence of the stream increased in power, by the currentbeing drawn from both shores and from the small arches, augmenting the volume ofwater, which was greater than had ever before existed. This corrosion at both sides of theold pier spread across the bottom of the locks adjoining, and attacked the stability of thestarlings under the old piers of the new arch; unfortunately the outer faces of thesestarlings were so close to the stone piers, and only 6 feet broad underneath the haunches ofthe great arch, that no pile engine could act, and there was but little space to stand andperform any efficient works. Mr. Smeaton was immediately called in, and he advised theonly probable remedy for the urgency of the case, which was to throw as much stone aspossible into the vacuities of the foundation, to preserve it from further corrosion;accordingly, the stones belonging to the old city gates, which had recently been pulleddown and sold, and which were stored up at no great distance, were repurchased and throwninto the gulf which had been formed from the deep water above to the deep water belowthe bridge. This remedy seems to have been suggested from the manner in which Gautierstates the bridge of St. Esprit to be supported, and maintained at a constant and greatexpense, yet the whole of the advice was not followed. Increased velocity formed ad-ditional danger, and eddies were thus created, in which all sorts of vessels became entangled.After a great deal of discussion, a compromise was effected between those who contendedfor having the current as gentle as possible under and through the bridge, and those whowere for maintaining as strong a current as might be, in order to work the water wheelsattached to the bridge. And the report further states, 4 ‘ that if the bridge was totallyremoved, and nature restored to its full power and original possessions at this place, therecannot be any doubt but the navigation would be here, as at any place upwards to FulhamBridge, free, open, and unencumbered for all the variety of craft which navigate thatextent of the river. Boats would pass up or down against the stream, equally as well asthey do now any where else; and a greater quantity of tidal water being admitted, by theremoval of that which obstructs its influx at present, the intercourse inland would be en-larged and extended by as much further as the tide would certainly flow’. The reflow ofthat newly and enlarged quantity' of water would scour out the sand shoals and muddyshores, and hurry off the filth produced from the common sewers, which through a certainsluggishness in the stream is not cleared away at present. The west country barges, andother large craft, would not be detained in certain parts of the river for want of water indry seasons. The upper end of the tidal water would swell the natural waters a long wayfurther up, and thereby release the craft from a demurrage, which increases the cost of thevoyage,—this question pervading the inland trade as far as Reading and Oxford. If thepass at London Bridge was free, the land floods of the Thames would have a ready passageto the tide way and the sea, and thereby pass off the useless superabundance more readily,and in such a manner that the shores and towing paths would be used, and barges passmore freely under the floors of the scaffold bridges at Chelsea, Fulham, and Kingston.The high waters of the tides respectively would be so much higher in this district, and thevelocity so much stronger upwards, that the voyage would be done in less time, and withmore safety, through a deeper water at each period of the tide. Some of the walls, itis true, would be found between this bridge and Kew not quite adequate thereto, andwould have to be raised by their respective owners.”

The area or space of water-way of the whole river at London Bridge before the same was