horizontal shaft carrying two 6-ft. spiral-grooved, cast-iron drums, around which the 7/8-in. steel-wire operating cables pass. As one of the lifting-ropes passes off the drum, the corresponding lowering-rope takes its place, and vice versa, the extreme horizontal travel being a little less than 12 in. Thus by turning the drums in one direction the span is raised, and by turning them in the other direction the counterweights are raised, and the span consequently is lowered. When the span is at its lowest position, the full power of one engine can be turned on to pull up on the counterweights, thus throwing some dead load on the pedestals of the span, after which the drums can he locked. Before the bridge was completed the writer considered that this would be necessary, in order to check vibration from rapidly passing vehicles; but such has not proved to be the case, for the span is very rigid, and the amount of the vibration is not worth mentioning. It is possible, though, that in some other lift-bridges, where the ratio of live load to dead load is greater, this feature of operation cannot be ignored.

The engines are provided with friction-brakes that are always in action, except when the throttle is opened to move the span; consequently no unexpected movement of the span is possible.

The raising-ropes, after leaving the drums, pass out of the machinery-house to and beneath some 5-ft. idlers under the towers, thence up to the top of the north tower, where they pass over some 4-ft. idlers and the main 12-ft. sheaves. Four of them here pass down to the north end of the span, and the other four run across to the other tower over more idlers, then down to the south end of the span.
      The lowering-ropes, after leaving the drums in the machinery-room, pass under some idlers below the north tower, and thence up to more idlers at the top of the tower. Four of them here pass down to the counterweights in the north tower, and the other four run across, over intermediate idlers in the overhead bracing, to the main 12-ft. sheaves of the south tower, then downward to the counterweights.

In addition to the previously mentioned method of moving the span by the water-ballast, there is a man-power operating apparatus of simple design in the machinery-house, which, when used alone, can raise and lower the span slowly in case the steam-power gives out, or more rapidly when combined with the water-ballast method.

As the span nears its highest and lowest positions, an automatic cut-off apparatus in the machinery-room shuts off tile steam from the cylinders and thus prevents the hydraulic buffers from being overtaxed.