The Northern Pacific farmer. [volume] (Wadena, Minn.) 1878-1885, 1883-11-15
A Wonderful Bridge.

A new bridge, whose structure seemA
most wonderful is to be thrown across
the River Forth five miles west of Edin-
burgh, Scotland. This has been in con.
temptation for years, but the width and
depth of the channel have, until lately.
proved too much for the engineers. It's
necessity is apparent. All the railroad
on the east side. of Scotland from tn.
south find terminus at Edinburgh;t
in order to make connection with
roads to Perth, Dundee, Inverness al
Aberdeen, it has been necessary cithe1
to 90 due west 25 miles to Stirling,
where the Forth is brigded, or to have
five miles ferry transfer across the
river just above Edinburgh.
The latter has been preferred in spite
of the occasional danger and inevitable
inconvenience of ferriage across road
stead of that width open to the easterly
winds. In these days of rapid transit
this is no longer endurable. The plan
adopted by the engineers, Messrs. Fow-
Ter and Baker, is striking example that
NECESSITY is the mother of invention"
The bridg will be stretched between
North and South Queensferry, six miles
above Edinburgh. At this point the
river is one mile and one-halI broad.
and half a mile from the north shore is
the small island of 1nchgarvield. This
would make com paratively easy prob
lem were it n vt that the depth Of va
ter precludes any piers for more than
half the distance. On the north the
channel is 2l0 feet. 1t is out Of the
question to try to sink calssons 50 far.
Sir Thomas Burch, who built the i'll
|cf. To hri1
sion. This would have required for the
cables two stone towers on the island,
each 500 feet in height, and on either
bank of the river one 5S4 feet high.
They can be better appreciated when it
is said that the towers of the Brooklyn
bridge rise but 27l feet above the East
river. The idea was speedily given up,
and the present one adopted. 1t should
be said that as yet it is only plan. Sew
eral hundred men are at work prepar-
ing the approaches, but the bridge is
| not yet constructed. The plans, how
| ever have been approved by the best
English engineers, and there is no rea-
son to appretend failure.
The principle is a very simple one.
| An ordinary pier structure runs out
little way On either bank. On the edge
! of the deep channel, near 9TH banks,
|
and similar cluster will stand On the
south side of the island. Upon these
three supports will rest the entire
weight of the bridge, Upon each one
will be poised an immense cap Of steel,
| made in tine form of an elongated lozen-
age, with the long axis representing the
line of railroad. The middle one will
rest on the four island piers, which Of
ford base 270 Ieet long. and will stretch
out>on either side 6S5 feet. The two
from the shore piers will come within
| $50 feet of meeting the centre one, and.
to fill the gaps and resting upon the
cages, two steel lattice girder bridges
will be hung. The middle cage will ex-
actiy balance upon its supports, but the
Their two will have to reach Oh further
over the channel than toward land,
and the balance will be made up by
weights. In order to live the neces-
sarv stiffness to such a span from
single base, the structure has to be stiff
ened in every manner. The plan of
the elongated lozenges gives each one
height above its pier $50 feet, sloping up
! from the pier and down from the top to
connecting lattice bridges. These loz-
enge shaped affairs are really steel cages,
! 120 feet wide at the bottom, and only
81 feet at the top. This inward slope
gives the strength of a trestle support,
for all the weight falls upon the piers
by uprights, and not by the arch prln-
ciple from the side. The upper sid Aof
the lozenges will be straight and the up
per ones curved. while the tracks will
run along their horizontal axes, l65 feet
above tie top of the piers, which will
also be the altitude Of the two connec-
ting steel orders, This balance, or can
tilever principle, has been used on large
bridges before, and its introduction here
will make one which will eclipse, as an
engineering wonder, the famous Brit
ANNA and Victoria tubular bridges.
Some idea of the magnitude of the work
can be gained by knowing that it will
take IS 900 900 and several years time.
At pr, sent the piers on the South side
are being put in, gigantic undertaking
in itself. On the north side they are
nearly completed. The bridge will be
of steel in every part except the piers.
It will thus be Eore costly, but lighter
and more durable. When done it will
work revolution in the manner Of
building long spans across deep water
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