( 32 )

supporting the ends of the untrussed girders
are to be carried. The want of a specifi-
cation alone would in strictness according
to the terms of the Prospectus, which re-
quires a "clear and comprehensive Speci-
fication" put the design out of the pale of
competition.

In No. 11 the abutments and approaches
are better than those of No. 10 and are suf-
ficient for the purpose, but in this design,
as in No. 10, the true principle of this es-
pecial mode of construction has not been
carried out. The wrought iron tube from
the comparative looseness of the connection
between it and the lattice bars, a simple
clip round the tube, to which the lattice
bars are "pinned" has no effect in stif-
ening the bridge, and it resolves itself into
an independent girder acting as a sus-
pension girder to the rest of the construction,
but as it is quite clear that it is not suffi-
ciently strong for that purpose, it might in
my opinion for all useful purposes have
been left out of the design altogether, thus
for want of the necessary stiffening or com-
pressing portions of the girders I have con-
siderable doubts whether it would possess
sufficient vertical strength. The essence
of the principle of the lattice bridges are
the string pieces and their firm connection
with the lattice bars or struts: the upper
string pieces are the straining beams of the
truss and these must not only be strong
enough in themselves to resist the compres-
sion to which they would be exposed, but
the struts must as in simple trusses abut
firmly and immoveably against the ends or
some intermediate point or points thereof,
which is not the case in the design. There
is no doubt of the tube being equal to the
compressive force that would be brought to
bear on a string piece properly connected
with the lattice bars (indeed two-thirds of
the sectional area of iron in the tube pro-
perly and firmly fixed, say similarly to the
wrought iron bars at the bottom of the
trusses, would have been sufficient) but in
this construction the tube would not be ex-
posed to compression but to a transverse
strain to which it would not be equal.
Considering therefore the doubts that may
be very reasonably entertained of the
strength of these girders, and also that the
true principle of this and all other trussed
constructions, into which lattice girders re-
solve themselves, has been departed from,
I cannot assign it a place amongst suitable
designs. I come to this decision irrespec-
tive of the probable cost of such a design
which I feel satisfied could not be executed,
for want of local facilities, competent work-
men, &c., for at least double the Estimate
made by the designer; indeed I will go far-
ther and express my belief that an iron
bridge on the most economical construction,
including abutments and approaches could
not be erected under an outlay of £3000.
Thus the designer of any iron bridge would
be under the conditions of the Prospectus
really devoting his time and talents without
the least hope of obtaining a reward for the
same by the adjudication of a premium.
Feeling this had the design last under con-
sideration been one that I could have re-
commended for adoption, and had the Esti-
mate accompanying it been fairly made
shewing approximately the probable cost,
I should have urged that the condition I
have referred to should have been waived
and one of the premiums been awarded,
even though the Provincial Government
could not have devoted the funds necessary
for its erection.

I now come to No. 12 to which I can-
not hesitate to assign the first place. It
displays evident careful consideration of
the subject in the general design and its
details, both in the drawing and in the de-
scription and specification; no essential
point has been neglected. Not that it is
an original design, for the designer in his
general preliminary description modestly
and candidly states the fact and quotes an
instance of its application; his merit there-
fore consists not in the conception but in
the adaptation of the principle and the pro-
portioning of the several parts to the lo-
cality and span. I may here remark that
most of the other designs are also imitations
of the other designs or of the prin-
ciples embodied in them, but unfortunately
the designers have failed in aptly carrying
out those principles, or in proportioning
their works to what they would have to
bear. Reverting to No. 12 I desire to
point out that the bow girders substantially
connected with the tie beams are amply
sufficient to support the roadway, so also
are the suspension bars, and the construc-
tion is stiffened and "undulatory motion
guarded against by the introduction of pro-
per strutting; lateral pressure has also been
met by horizontal strutting under the road
way; farther, the strutted beam across the
small span is fully equal to its duty. It
is only to be regretted that the designer did
not boldly span the whole stream at once
instead of proposing the erection of a pier
which pro tanto would diminish the
water way even at the ordinary level of the
river, and might in floods form a serious
check to the free passage of large trees; he
has not however departed in this respect
from the conditions of the Prospectus.
Two, not precisely defects or affecting the
principle or strength of the bridge, but
still matters which I deem it necessary to no-
tice, I must draw attention to. One is that