XCVI. PERCY ALLAN. 
A provision for such adjustments (Plate 3, fig. 1) is of considerable 
importance in this type of bridge, the correct centring of towers 
being specially necessary for the satisfactory working of lift span. 
Over each pier are seated two transverse girders spaced 17” apart, 
the webs being connected with four diaphragms, and the top and 
bottom flanges, with chequered plates and flat diagonal bars 
respectively. Between the transverse girders over each pier, are 
fitted, two longitudinal girders spaced 13’ 7” apart. A lateral 
strut at centre of longitudinal girders with four diagonal tie rods 
completes bracing of the tops of the four towers. (Plate 4) 
The lift span is counter weighted with four cast-iron balance 
boxes, working on steel V guides bolted to the outside angles of 
towers. (Plate 3, fig. 2) The balance boxes (each in eight sections, 
filled with lead) are carried by wrought iron adjustable suspension 
rods, to which are spliced the sixteen 24” steel galvanised wire 
ropes—four to each box—which pass over the rope wheels placed 
over the top of towers and are then connected to steel suspension 
brackets bolted to the four corners of lift span. The lift spam 
“hangs” clear when being raised, but provision is made for 
“swaying” by placing two rollers at each corner of span to take 
bearing on a bull headed rail bolted to angle irons of towers. 
The machinery platform (Plate 3, fig. 2) is placed downstream at 
the same level as kerb of side spans. 
Although provision is made for working with two men, the 
bridge as a rule, will be operated by one man working 4 wineh- 
handle (Plate 3) on a horizontal shaft inside the towers, carrying 
a pinion gearing into a spur wheel keyed to a second horizontal 
shaft which is connected by mitre wheels to a vertical shaft pass 
ing up the inside of and through the top of towers, the vertical 
shaft being connected by bevel wheels with a short horizontal shaft 
at the top of towers, (Plate 4) carrying a pinion gearing into ® 
spur wheel keyed to the downstream longitudinal driving shaft, 
to which is keyed at each end a pinion gearing into teeth cast oe 
the inside of rim of the two rope wheels over down-stream tow 
Pinions are also keyed to ends of upstream longitudinal shafh = 
