454

HISTORY OF ENGINEERING.

Book I.

those in front. The horizontal joints to be rusticated, and to be in every respect executedin tlie same manner as the spandril walls and buttresses over the piers, the whole to be setin mortar hereinafter to be described.

“ Waterman $ Stairs .—The walls above the level of the springing of the-arches are to beexecuted as described in the drawings; they are to be composed of the best hard grey stockbricks for the interior, the exterior to be composed of the best granite, as before described,and in courses of not less than 15 nor more than 21 inches thick, laid header and stretcheralternately, and average depth in the bed of not less than 3 feet 6 inches, the upper bed ofeach course to be dressed smooth and even before the next course is commenced, and thehorizontal joints are to be rusticated as before.

“ Interior Spandril Walls _Previous to these spandril walls being commenced, the whole of

the joints on the back of the arches and of the inverted arches are to be well cleared out, and ifany opening can be found it is to be properly filled with grout, and afterwards the joints are tobe well and firmly pointed with Roman cement, and the whole surface of the arches betweenthe termination of the inner spandril walls on each side of the crown of the arches to be coveredwith a sufficient coating of Roman cement of the best quality; the interior spandril wallsare to be composed of the best hard well-burnt grey stock bricks, laid flush in mortar ofthree parts clean sharp river sand to one part of well-burnt Merstham, Dorking , or otherlime equally good; the interior mortar to be composed of four parts of sand to one part oflime; these are-to be six in number over each pier, and to extend from arch to arch, thewalls to be 2 feet 3 inches thick; on the tops of these walls are to be stone corbels 18inches deep, projecting on each side over the walls not less than 12 inches, and there are tobe corbels projecting 12 inches from the inner side of the retaining outside spandril walls;these are to be composed of Bramley Fall, Painshaw, or Derbyshire stone.

“ The whole surface over these walls, and for 1 foot on each of the retaining or outsidespandril walls, to be covered with good strong Yorkshire landings not less than 9 inchesthick, the longitudinal joints in all cases to be over the centre of the interior spandril walls :these coverings are to be fair-dressed, and close and well-jointed, and firmly and solidlybedded on the corbels underneath, in mortar hereafter described.

“ Roadway over the Bridge .—When the whole of the arches and spandril wall coveringshave been carried up to the level for receiving the roadway, the whole surface of the bridgeis to be covered with a bed of sound, tough, well-beaten clay, 15 inches thick, thoroughlypuddled, and well-beaten together, so as to become perfectly impervious to water. Theclay is then to be covered with 3 inches of fine sand; there is then to be a course 12inches thick of fine flint stones, broken into small pieces, so that none are to be larger insize than 2 inches diameter : the whole is then to be well-dressed and rolled. The footpaving is to be composed of granite, as before described. These stones are to be the wholelength of the footpath, that is, 7 feet 6 inches long, 8 inches thick, and 3 feet and upwardswide; on the one end they are to be properly bedded on the cornice ; and at the other endthey are to be supported by curbstones not less than 4 feet long, 9 inches wide, and 12inches deep, set edgeways, to be of the best granite, as before described, and properly beddedand jointed, and set in mortar. The intermediate spaces are to be filled with fine gravel orsand, so that the paving may be bedded throughout. Along the front of these stones thereare to be gutters or watercourses, paved with granite pitching paving 9 inches deep oneach side, for the width of 5 feet 6 inches from the outside of the foot paving. It must beobserved that the roadway is to be curved 6 inches in its transverse direction, and theclay and pavement is to incline inwards towards the gutters, as shown in the drawings.

“ Cornice and Parapets . — The cornice and parapets are to be constructed of the bestgranite, as before described, and are to be executed in every respect agreeably to thedrawings; they are both to be finely dressed and jointed ; none of the stones belonging tothe cornice, plinth, dado, or coping of the parapet to be less than 4 feet 6 inches long, andto be bonded and dowellod properly over each other, the coping to be dowclled at everyjoint by a projecting dowell 2 inches square, fitted into an equal recess in the adjacentstone. All the stone is to be perfectly free of blemish and deficiencies of any kindwhatever.

“ Approaches. — The approaches are to be formed of solid embankments and arches wherethe height will admit, as shewn in the drawings ; in the former case the embankments areto be supported on the sides with brick retaining walls, as shown, and where arches areadopted the piers are to be founded 6 feet below high water mark, according to the TrinityHouse standard, and the retaining walls 3 feet below the said high water mark ; the un-sound earth, for at least 6 inches below, is to be removed, and to be replaced with soundgravel and lime, in the proportion of five parts of the former to one of the latter, to be wellmixed and puddled together, and to be allowed time to harden ; there is then to be laidYorkshire landings G inches thick, and not less than 2 feet wide, and at every 6 feet to be4 feet wide each for the whole width of the foundations; upon the top of these landingsthere is to be laid a course of Bramley Fall, Derbyshire, Painshaw, Red Castle stone, 15inches thick, 4 feet wide, and not less than 4 feet long, to be so laid as to break bond over