REPORT ON HYDRAULICS. PART II. 501 



The surveys which have been made under the direction of the 

 late Mr. Rennie, by order of the Lords Commissioners of the 

 Admiralty and of the Corporation of the City of London, both 

 above and below bridge, at different periods, and also by Mr. Tel- 

 ford previous to the building of New London Bridge, have left 

 ample data of the course and sections of the river Thames ; but 

 no measures seem to have been adopted to ascertain the effect 

 which the removal of the Old London Bridge was likely to 

 occasion in the operation of the tides ; and, as before stated, 

 opinions being very contradictory, it occurred to Messrs. Rennie 

 to institute a series of observations for that purpose. 



Accordingly, the new bridge having been opened to the public 

 in the year 1831, the demolition and total removal of the old 

 bridge commenced on 22nd November following; and on the 

 25th, Mr. Combe (Messrs. Rennie's assistant) was instructed by 

 those gentlemen to proceed up the river to collect information, 

 and to make preparations for establishing a series of observations 

 at Putney, Kew, and Richmond Bridges, and at Teddington 

 Lock. Tide-gauges accurately adjusted by levelling to a tide- 

 gauge similarly fixed at New London Bridge, and at Fresh Wharf, 

 and a little below the bridge, were therefore fixed at these 

 places, and experienced persons were appointed to keep a daily 

 register of the high- and low-water marks as indicated by the 

 gauges. Accordingly, everything being ready by the 30th of 

 November, a simultaneous commencement was made at the dif- 

 ferent places on the 1st of December, and the observations were 

 daily recorded in a book kept by each person and forwarded to 

 London every ten days, until the first of June 1832 ; and in order 

 to prevent any mistakes, the gauges were frequently visited 

 and inspected, and upon every occasion Mr. Combe found them 

 undisturbed and each person attentive to his duty. Up to the 

 first of June, however, scarcely any part of the bridge which 

 obstructed the waterway had been removed, with the exception 

 of two piers which had been cleared away for the accommoda- 

 tion of the craft navigating upwards during the building of the 

 new bridge, the works of which nearly compensated for the en- 

 largement of the waterway under the old bridge. These alter- 

 ations had, however, lessened the fall at low water about one 

 foot. 



The flood or low water in the early part of the year having 

 been found to intei'fere so much with the free action of the tides, 

 and as at the commencement of the year 1833 there was a consi- 

 derable fresh in the river, it was deemed unnecessary to resume 

 the observations until the beginning of the month of March; at 

 which period, however, both in the year 1833 and 1834, the 



