RAILWAY EXTENSION IN AUSTRALIA. 983 
to do so; yet no one seriously proposes to close half the railways 
on this account. 
The conclusion, drawn, therefore, is, that generally, in easy 
country, the working expenses for a light traftic, with interest on 
capital, need not exceed about £4 per mile per week, and 
taking passengers and tons of goods as units, and including 
traffic in both directions, it would only require the saving in 
transport of less than 6,000 of these units, annually, to repay 
expenses and interest. All traffic above that, besides what may be 
called the direct credits, before enumerated, would be to the good. 
This figure, 6,000, is not much more than a third of that ofti- 
cially estimated as supplying, on an average, the traffic on each of 
the five lines referred to. 
Notwithstanding this encouraging way of estimating the value 
of future railway extension by the colonies, a word of warning is 
uttered against costly extension into poor districts, and also short 
branches, which are specially expensive to work ; and the paper 
concludes by pointing out that the treatment of the subject is 
limited, in it, to the usual case of railway superseding road 
carriage. Sea, river, or rival railway competition, give rise to 
different figures and to the conclusions based upon them, though, 
of course, the principle is the same. 
No. 3.—ON THE RAPID ERECTION OF A STEEL VIA- 
DUCT TO REPLACE A TIMBER STRUCTURE ON 
THE NEW SOUTH WALES RAILWAYS. 
By Watrer SHettsHearR, M.1.C.E. 
(Read Saturday, 8 January, 1898.) 
[ Abstract.] 
THE paper describes the work of renewing Nos. 3 and 4 of the 
series of timber viaducts across the Muriumbidgee River flats 
flanking the fine iron bridge over the river. 
On the north side of the river, the viaducts consisted of No. 1 
(112 spans), No. 2, (65 spans), No. 3, (4 spans), No. 4 (71 spans), 
and on the south side, No. 5 (57 spans), and No. 6 (4 spans) the 
span in each case being 29 feet 6 inches, the total length being 
9,263 feet of timber work. 
