LIFT BRIDGE OVER THE MURRAY AT SWAN HILL. CVIIO 
of lift span over the rope wheel at top of tower, round which the 
rope takes a complete turn, passing thence across to, and over 
the rope wheel on opposite tower, Shoo end of rope being made fast 
to counterweight. 
In the Chicago Bridge, the supporting ropes at each corner of 
Span passed over the sheaves at top of tower and were then attached 
to the counterweights, this being the ordinary means adopted of 
counterbalancing a lift span, the operating ropes were however 
crossed over the waterway similarly to the Bourke arrangement, 
but instead of taking a complete turn over the sheaves, the “turn 
was taken over the driving spiral drum at foot of tower, idle 
pulleys being interposed to change the direction of ropes as 
required, before attaching to counterweights. 
Mr, Allan was pleased that Mr. Haycroft was so thoroughly 
in accord with him, as to the features of the truss adopted for 
the side spans of the bridge, which had so far met all that he 
(Mr. Allan) had claimed for this type of truss when introducing 
it in 1893, 
Mr. Grimshaw had referred to the timber in the structure— 
Mr. Allan said tallow wood planking and ironbark for the 
remainder of the work had been specified, it being out of the 
question, with the small scantlings employed, to use other than 
ironbark for the truss spans, as will be seen from a glance at the 
following table, compiled from Professor Warren’s work on 
Australian timbers : 
IRONBARK AND MURRAY RIVER RED GUM TIMBER. 
AVERAGE Srrenora IN Pounps PER Square INcH. 
| 
Transverse § Strength. 
Modulus of Elasticity. 
Timber —, . —— -_ 
; Speci- percentage) Speci 
Average | | Seeeee sh arse 
mons | Averige lot irombark| meng | strength. | verre 
a 
——— an Sa 
Ironbark ... | 28 2,635,470 926 | 28 | 18,204 61°6 
| 
RedGum ...__...|_ 3. {1,873,542)_... 3 | 11,267 
