give great transverse rigidity to the structure, and at the same time afford ample support for the caps. A good spacing is as follows: Distance centre to centre of outer piles, 11' 0" ; distance centre to centre of two inner piles, 4' 6".

The caps should be at least 12" X 14" X 14', placed on edge and attached to the piles by means of 8" drift-bolts.

For ordinary pile-trestles in fairly firm soil no longitudinal sway-bracing will be required for heights below ten feet; but for heights between ten and twenty-two feet, single-deck, longitudinal sway-bracing should be used in every fifth panel, so as to prevent the structure from moving longitudinally as a whole because of thrust of trains. For heights greater than twenty-two feet, each alternate panel should be braced longitudinally by double-deck bracing, so as to hold the piles at mid-height, and thus strengthen them as columns; the transverse sway-bracing for these cases should also be double-deck for the same reason.

For ordinary pile-trestles up to twenty-two feet in height the panels should be a trifle less than fourteen feet in length, while for greater heights either the same length may be used or alternate panels may be made from twenty-four to twenty-eight feet long by trussing the stringers, according to which of the two methods is the more economical.

The stringers under each rail should be built of three runs of timber, generally sixteen inches deep, the sizes being determined from the loading and by using an intensity of two thousand pounds for the extreme fibre, when impact is included. The stringer timbers are to be separated from each other at the panel points by means of timber packing-blocks, which are to serve also as splice-timbers. These timber blocks should be at least three inches thick and six feet in length, and should have at least four bolts through them. They are to be separated from the stringers by small cast-iron fillers three quarters of an inch thick, so as to prevent the timbers from coming in direct contact with each other. The splice-timbers must be made wide enough to project an inch or two below the bottoms of stringers, and must be notched over the  caps  so  as  to  hold  the  stringers  firmly in place.  The distance