266 Transactions.—Miscellaneous. 
pelled engineers to avail themselves of the principle, and now skew arches 
are to be met with on nearly every line of railway in Great Britain. 
Bridges in Otago. 
In a colony like this, bridges as a rule have hitherto been constructed of 
timber. This is owing to the rapidity and cheapness with which such works 
can be carried out, and the circumstances of a young colony seem to justify 
such economy. But I question whether there is in this any real economy 
in the long run. For even where the workmanship is of the best and 
the quality of the material unexceptionable, timber bridges require constant 
repairing, and cannot at most be expected to last more than fifteen or 
twenty years. Iron bridges are no doubt very convenient in railway works 
and for great spans, but even they are not equal in durability to good stone 
arches. This fact has caused the Parisians to substitute arches of masonry 
in their main thoroughfares, for the iron bridges previously erected there. 
English engineers are coming round also to admit, that stone after all, has 
many advantages over iron in permanent structures. Most of the bridges 
recently built in Otago by the Provincial Government are a great improve- 
ment on timber pile bridges, as the piers and abutments have been built in 
masonry, the superstructures only being in timber. The only stone arches 
however, of any importance, which Otago at present possesses, are those on 
the Main North Road from Dunedin to Oamaru, five in number, and two or 
three on the road from Palmerston to the interior; the greatest span of any 
one of these being sixty feet. There are no skew arches in Otago and I am 
not aware of the existence of one in any part of New Zealand at present. 
On bridges in Otago there was spent by the Provincial Government, 
during last year alone, no less than £34,751, so the kind of material which 
is best for their construction is a consideration worthy of the attention 
of all good colonists. 
Skew Arches. 
I will now proceed to describe the principles and construction of skew 
arches in masonry, illustrated by drawings, and a small model of an actual 
segmental arch, built seven years ago. These drawings are No. 1, and 
No. 2, appended to this paper: No. 1 shewing half elevation, plan and 
section ; and No. 2, the development, on a flat surface, of the intrados and 
extrados, which is the more important and necessary drawing for the 
guidance of the builder. 
Definition. 
A skew arch in masonry may be defined as being an arch whose abut- 
ments are equal, parallel, but not directly opposite each other, and whose 
courses, from face to face, are not parallel but inclined to abutments, and 
are spiral surfaces, The angle of skew, 0 on Drawing No. 1, is the angle 
