450

HISTORY OF ENGINEERING.

Book I.

posed of ashler, in courses of not less than 15 inches nor more than 21 inches thick in thefront, and the beds in the interior are to incline parallel backwards, as shown in thedrawings; but the courses next to those under the springing of the arches are to be of thethickness and projection as shown in the drawings. The exterior stone, for an averagedepth of 5 feet 6 inches to within 3 feet below the springing of the arches, is to be com-posed of the best English, Scotch, Irish, Jersey, or Guernsey granite, to be approved ofby the principal engineer ; the interior stone is to be composed of one half of the bestBramley Fall, and the remainder of Painshaw, Derbyshire, or other stone equally good.

“ The masonry is to be formed of header and stretcher courses alternately ; the headers tobe on an average 5£ feet long, but not less than 4.1 feet long, and of the average breadthof 3 feet, but no stone to be less than 2 feet 3 inches wide.

“ The stretchers to be on an average 5 feet long, and none less than 4 feet, and an averagewidth of 3 feet, but none to be less than 2 feet 3 inches wide. The backing or heartingto be laid in courses of headers and stretchers alternately, the headers being opposite to thestretchers in front, and in size and thickness suitable thereto, so that the whole masonry,exterior and interior, may be completely solid and bonded together throughout every part,and double joggles to be used where and when considered necessary by the principalengineer, according to the mode shown in the drawings, and the upper bed of each courseis to be dressed off smooth and even before the next course is commenced. The whole ofthe exterior stone is to be smooth and fine hammer-dressed on the face.

“ The horizontal beds arc to be fine dressed and rusticated 2 inches each way; but theupright or vertical joints are to be plain and perfectly straight and fine dressed for at least15 inches inwards; the remainder of the stone to preserve its full dimension, and to befine picked and straight between the whole of the backing or hearting, to be straightdressed in the beds and joints, and the upper bed of each course to be dressed ofT smoothprevious to commencing the next course; all the backing belonging to each course isto preserve an equal thickness, and upon no account must it be permitted to run onecourse into another, except where joggles or dowels arc directed to be used; the wholeof the above described masonry is to be set flush in beds of the respective kinds of mortarhereinafter to be described, and properly grouted.

“ The masonry of the piers up to the springing of the arches is to be built or composedof ashler, laid in horizontal courses of not less than 15 nor more than 24 inches thick,except the course next to those under the springing, which is to be of the thickness andprojection as shown in the drawings. The whole of the exterior stone for 5 feet 6 inchesinwards, except within 3 feet of the springing (which is to be of granite), is to be composedof the best granite as before described. The interior stone is to be composed of one halfof Bramley Fall, and the remainder of Painshaw, Derbyshire, or other stone equally good.

“ The masonry is to be formed with headers and stretcher-courses alternately, the headersto be on an average 5^ feet long, but none less than 4^ feet long, and on the average breadthof 3 feet, but none less than 2 feet 3 inches. The stretchers to be on an average of 5 feetin length, and none less than 4 feet long, and an average width of 3 feet, but none to beless than 2 feet 3 inches wide. The backing or hearting is to be laid in courses cor-responding in thickness with the outside courses of ashler, header and stretcher alter-nately, the headers being opposite the stretchers in front, and in size and thickness suitablethereto, so that the whole of the masonry, exterior and interior, may be solid and bondedtogether throughout every part, and dowels and joggles are to be used where and whenconsidered necessary by the principal engineer, and the upper bed of each course is to bedressed off smooth and even before the next course is commenced ; the whole of theexterior stone is to be smooth, and fine hammer-dressed on the face ; the horizontal beilsare to be perfectly straight and fine dressed, and rusticated 2 inches each way, but theupright or vertical joints are to be perfectly straight and fine dressed for at least 15 inchesinwards ; the remainder of the stone to preserve its full dimensions, and to be fair pickedand squared between. The whole of the backing or hearting is to be fair dressed on thebeds and joints, and the upper bed of each course is to be dressed off smooth ; andprevious to commencing the next course, all the backing belonging to each course is topreserve an equal thickness, and upon no account must it be permitted to run one courseinto another, except where joggles or dowels are directed to be used ; the whole of theabove described masonry is to be set flush in beds of the respective kinds of mortar herein-after to be described, and properly grouted.

“ Tike stair walls to the level of the springing of the arches. These walls are to be con-structed agreeably to the drawings, and to be composed of hard, well-burnt stock bricksfor the interior; the exterior, to the level of the bed of the river or adjoining ground, tobe composed of the best Bramley Fall stone or other stone equally good, laid in coursesnot less than 15 nor more than 24 inches thick, to be laid header and stretcher alter-nately, and on an average depth, the bed not less than 3 feet 6 inches, and above the bedof the river, to the level of the springing of the arches; the exterior to be composedof the best granite as before described, and in courses not less than 15 nor more than