case of the strained cables and for the single-loaded arm are identical, hence it is proved that one end of a draw can rise when the other arm is loaded and when the longitudinal tower bracing is incapable of carrying any vertical shear past the pivot-pier.

In erecting draw-spans, some method of adjustment must be provided so as to bring the ends to the correct elevation. For comparatively short spans, say up to 200 or even 250 feet, groups of thin plates on top of piers will suffice, as the grade can be adjusted by dapping the ties or joists; but for longer spans there will be needed in addition to this method an adjustment in each of the bottom chords by the insertion of several thin transverse plates in the panels next to the drum.

The tops of all pivot-piers should be so designed as to drain thoroughly by pitching the upper surface from the centre towards the periphery, and by providing at the latter weeping pipes that pass below the lower-track segments.

In large, heavy drawbridges all parts of the turntable and machinery should be made much heavier than the corresponding parts for smaller structures, even if there be no theoretical reason therefor; because the tendency in the past has been to design all portions of the machinery for the exact amounts of work that they are assumed to do, which method gives for many pieces sizes entirely inadequate for some conditions of stress to which they are likely to be subjected. The proportioning of turntables and machinery for draw-spans is a matter involving good judgment and experience in operation rather than intricate mathematical calculations.

The author desires to call attention to the necessity for making all man-power machinery extra strong; because, if there be anything wrong with the apparatus which prevents it from operating properly, the men are liable to crowd upon the levers wherever they can find room, and then surge thereon to their utmost capacity. It was only a short time ago that in operating the East Omaha draw by hand two sets of six or seven men on each of the two four-armed levers failed to start the span in motion. Immediately upon finding the unexpected resistance,  they  all  stepped  back  a  few  feet  and  threw  them-