XVI. DISCUSSION. 
form of the bridge. After the trusses are erected then the 
platform should be added. The old practice used to be on the 
interlacing principle, leading to something like a Chinese puzzle, 
and very difficult to deal with in case of renewal. Another point 
to be considered was the replacement of the separate pieces of 
the truss, one or other might decay, and they ought to be so 
fixed that these particular pieces could be easily taken out, and 
what was of great importance, was the construction of the joints, 
so that there should be no lodging of water in them, and that 
they could be examined, and attended to when necessary. With 
regard to the comparison of the cost of the bridge, the illustration — 
of which the speaker exhibited, with that of Mr. Allan’s, the 
conditions were different, as his was intended for road traffic, and 
the other for railway purposes. In the road bridge one of the 
largest items of expense was decking, which the railway bridge 
was made very much narrower, but having to carry heavier loads 
was much stronger. 
Mr. Burce—He intended to refer to-night only to the author’s 
comparison between the ultimate cost of timber as against iron 
or steel in bridge construction. With regard to the cost of the 
two kinds of structures, a comparison of which was shewn in 
the table exhibited, the quotation for iron was for colonial manu- 
facture. It might be the view of some people that it was a wise 
thing to pay something extra in order to encourage manufacture 
in the Colony, but the extra amount so given was given for that 
purpose only, and it should not be added to the actual cost of the 
bridge. Moreover, there was no doubt that Mr. Allan had 
proved his case, without thus surcharging the ironwork with 
regard to the preference of the timber over the iron bridge, but — 
if we came to smaller bridges the difference between the per- 
manent design and the temporary one was not so great. In 
preparing railway estimates he had made the following caleula- 4 
tions, which illustrated these views :— 
Comparison of timber as against permanent bridge work 
assuming no repairs to latter, and in the former about one-fifth, 
