HISTORY OF ENGINEERING.

466

Book I.

depth opposite to each joint, others of the same thickness and half the breadth are to bedriven, and then the whole firmly united by walings and iron bolts.

“ The piles driven inside, and which support the foundations, arc to be made of beechor newly-cut Scotch fir cleared of its bark, shod and hooped as before described; afterthey are driven to a bench mark, all the heads to be cut oil’ to an exact level, to receivethe sleepers and the timber platform; but before this is established, the soil is to be taken

Fig.46S

GLASGOW BRIDGE,

out between the heads of the piles to the depth of 1 foot or more, and the space filled inwith hand-set rubble, well packed, and laid flush in good water-lime mortar.

“ Foundation sleepers -Upon each transverse row of piles is to be laid a sleeper, extending

across the whole width of the pier or abutment, secured to the head of each pile by awrought-iron ragged bolt of jj-inch round iron, 15 inches in length or more, accordingto the depth of the sleepers, and between each row of sleepers filled in with hand-setrubble, laid in good water-lime mortar.

“ Platforms. — Upon the sleepers are to be laid two floors of Dantzic, Memel, or Ame-rican red pine planking, to cross each other at right angles, spiked down with long spikes,and firmly united to the sleepers.

t( Masonry —After the foundation platforms arc completed, then the mason to commencewith his work.

“ Dressing of ashlar. — The whole of the stones which compose the piers and abutmentsmust be truly squared throughout, and should have chisel drafts round the faces, beds,backs, and end joints, and be truly pick-dressed down the drafts. The outside face work,from the bottom of the foundation to the level of low water line, should be broached inhorizontal lines, not coarser than eighteen to a foot.

“ Granite facings should be of uniform colour and quality, and laid in alternate courses ofheaders and stretchers; the headers, where they have 2 feet in length of face, are to have asmuch on the bed ; the stretchers should be 6 inches longer, and not less than a foot inwidth on the bed. Each stone should be truly squared, and fair dressed on the beds andjoints, full throughout, the backs scapelled, and the fronts rough picked ; the front arrisbeing axed or chisel drafted, so as to make a close joint on the face.

“ Ashlar hearting. —The hearting masonry to the piers or abutments to be squared ashlar,well dressed, and laid in courses of uniform thickness throughout, and agreeing with that of