The best style of bracing for both the longitudinal and transverse faces of the towers consists of stiff diagonals, each formed of four angles with a single line of lacing, all of said diagonals being riveted to the columns and to each other where they intersect by means of plates, and no horizontal struts being used except at top and bottom of towers, where they are necessary to make the bracing a complete system. The panel-points of the longitudinal bracing should coincide with those of the transverse bracing, although near the top of the tower the panels of the latter may be divided on account of the small distance between columns.

In cheap structures, expense can be saved by making the diagonals of the sway-bracing of adjustable rods, and putting in horizontal struts at the panel points, which struts should always be riveted at their ends to the columns; because pin-connected struts do not stiffen the columns sufficiently to warrant the figuring of the latter as fixed at the panel points.

When adjustable diagonals are adopted, the employment of horizontal struts at top and bottom of towers on all four faces is even more imperative than it is when stiff diagonals are used. The author has seen trestles without such bottom struts, in which the columns have been moved considerably out of place by the rods contracting in cold weather and drawing the column feet together. Six months afterwards the rods elongated and hung in festoons, so were promptly tightened up by the bridge inspectors, thus putting them in good condition to repeat the operation six months later, and so on from year to year till the columns were bowed perceptibly out of line.

In all towers, in each plane of the main panel points of the bracing there should be a horizontal system of diagonal adjustable rods to bring the columns and tower to place and line and to retain them there. The use of these systems of horizontal bracing is a sine qua non in scientific designing, for their omission will permit the faces of the tower to get out of plane, and thus the metal in the columns will become overstrained.

Whether it is better to arrange the column feet of towers so