The Sun.
London, England, 1864-05-20 00:00:00

THE BRIDGES AT BLACEPRIARS,

The works connected with the magnificent rail-
way bridge for the London, Chatham, and Dover
lino across this part of the river are now so rapidly
advancing towards completion that even the casual
ohserver can mark the progress made from day to
thy. Never even in London has a work of such
magnitude and such solidity been executed in so
short time. On the 2d of May last year the first
stone of the Surrey abutment was laid, and on the
31 of this month the last stone of the masonry on
the Middlesex side was completed. The line up to
the Holland-street side has been finished, and ap-
preyed by the Government inspector, and will be
opened for traffic on the Ist of next month. Of
the bridge which will connect this great goods
station with the City terminus, two of the wrought-
iron spans are completely finished and standing
alone ; the supports will be removed from the
third next week, and the fourth and fifth are well
began, and will be completed in the course of a
month or six weeks at latest. The preliminary
tests for strain w:11 then be made by loading the
whole work with locomotives placed as close together
en all four lines of way as they can stand, and
then the bridge will be formally opened into the
temporary station at Ludgate-hill in the middle or
end of August next.
The extreme rapidity and simplicity of the mode
in which these huge wrought iron spans are built
in
place is just now curious to witness. Each span is
160 ft. long by 16ft. deep, and laid for two lines of
rails ; two such spans laid side by side form the
width of the structure, which is five spans, or a little
short of 900 ft. long. The method of building it is
by constructing what is called an American truss—
that is, a powerful lattice work of timber strength-
ened with iron tie-rods in every part ;in fact, nei-
ther more nor leas than the cheap strong frame-
work on which the Americans carry all their rail-
roads across rivers. This truss, which is floored at
the bottom, and strong enough, to bear a load of
three tons per lined foot, is built with its endsrest-
in g jnat below the heads of the iron piers which are
to carry the permanent girders, the broad iron plates
of the bottoms of which are then laid in place on
beams of timber to raise them from the floor of the
truss to just above a level with the heads of the
columns, and whets fitted are loosely keyed together.
Once thus keyed in, the angle ircna at the sides are
rivetted on to prevent any lateral movement, and a
sound basement got at once on which to proceed
building up the cross-barred pieces, which can now
be seen in the finished spans, and which form the
struts and tie-rods, one to resist compression and the
other to meet the tensile strain. When these have
been raised to their full height of left. the top flange
is fitted, keyed, and rivetted together simultaneously
with that at the bottom, and the span is complete and
ready to stand alone, though still resting on the
beams, which we have spoken of as supporting it on
the floor of the truss. When the last rivet has been
driven these beams are knocked away, and the
girder stands alone supporting its own weight, and
equal to any that is ever likely to come upon it,
for each span is built six times in excess of the
strength required to resist the proof strain which
will be put upon it by the Board of Trade, and
which proof strain is itself calculated at more than
four times what the ordinary exigencies of metro-
politan railway traffic will ever bring upon it. Each
span is built with what is termed a five-inch cam-
ber—that is, it is arch-shaped, but the rise of the
arch is only five inches. When the last supports are
removed from under the span it comes down at
once two inches from its own weight of 600 tons,
and, instead of rising five inches towards the centre,
it only rises three. This diminution of rise is caused
by the strain of its own weight, and is produced by
an infinitesimal but general compression of all the
plates in the top flange we have spoken of, which at
once brings the structure to what are called its bear-
ings—that is, to a point beyond which its further
yield will be almost imperceptible, even under the
most ponderous weights. When a span has thus
been completed and left to stand alone, another
American truss is built for the reception of the next,
and so on, till all the five spans of the bridge get
into various stages of progress at the same time.
Each span as we have stated, consists of two of these
ribs or girders laid side by side—that is, there are
two outer-rib girders, on which rest the crossbeams
for the floor, and the end of these crossbeams meet
on a middle girder, which has thus to do extra duty,
and has therefore to be of proportionately extra
streogth. All three girders are of the same depth,
but the two outside have only a width of 3fe, while
the middle one has a width. of 41t. 6in. The tie-
rods and struts are placed at intervals of about4ft.
apart. The former are flat bands of iron, half an inch
thick, and varying in width by gradualincreases as
the end of the lever is approached, end the strain
becomes heavier, from five inches wide to ten. The
struts may be known at once by th lattices work of
iron between them to prevent their buckling or
moving in the slightest degree out of the line of the
compressive strain they have to meet. On the ties
there will be a tensile strain of five tons. on the
struts a compressive weight of three tons, and some
have been tested to six times that amount before
being put up. The cross floor between these ribs
or girders is of equal strength. These cross girders,
all of wrought-iron, are at intervals of only four
feet apart, to correspond with the ties and struts,
while throughout the whole length of the bridge,
from end to end, ran longitudinal girders placed so
as to support each rail of the permanent way. Thus,
therefore, the cross girders or beams of the floor
being placed at intervals of only four feet apart, and
being again intersected by the longitudinal beams
h ch carry the rails. divide the whole floor into a
series of square compartments of wrought-iron of
great depth and of proportionate strength. Over
this cellular framework will be laid a thin wrought-
iron floor covered with asphalt, and over all the
sleepers and ballast for the roadway. Each pair of
main ribs or girders is connected from the upper
flanges by cross ties, three to each span,which are
placed more to guard against lateral vibration than
anything else. The ends, too, of each pair of spans
where they reach the columns are left quite unfast-
ened, resting on roller frames. This leaves each
span to contract or en Aid as freely as the weather
may require, but the greatest difference between the
extreme of summer heat and depth of winter wilt
only make a difference of from 21in. to Sin. in the
length of the whole structure. Where these ends
of the girder-ribs meena very handsome raised cast
panel, to be hereafter gilt and coloured, will conceal
their junction. Nearly all the lower works of the
piers and groups of cast-iron columns is finished,
only one grow., of columns on the Middlesex side
remaining to be placed, and these will be on end in
the course of a week.
The completed piers on the Surrey-side come out
with a remarkably bold and imposing effect now
that they are finished. Not the slightest subsidence
has taken place in any of these piers, though one
has been weighted to more than double the strain
which the group of three will have to carry. In fact,
with their foundations going 29 feet deep in the
London clay, nothing short of an earthquake could
now disturb them. The Surrey side station is
nearly finished, and all the buildings and arrange-
ments connected with this are as complete as regards
the facilities they offer to the public as the other
stations along the line to Victoria. They are lite-
rally models of what such metropolitan stations
ought to be. The traditional clay-coloured timber-
shed hos been repleced by lofty and ample waiting
rooms for first and second class passengers, and the
rooms themselves are not only solidly, but even
comfortably furnished. Oa the Middlesex side the
station in Bridge-street is progressing, and all the
foundations up to Skinner-street, Snow-hill, are
placed. The abutments for the Ludgate-hill viaduct
are complete, and the beautiful iron work of this
formerly much-abused structure will be in place in
another month, Each side of this bridge will carry
a light and handsome outer bridge for foot passen-
gers, communicating with a staircase in the abut-
ments, which will lead down to Ludgate-hill,
That hideous eyesore—the wall of old Fleet Prison
will be removed, and its place occupied by a hand
some station, similar in its general appearanc,
decoration to that on the Surrey side of tn,
TrDica,,,s. In Brifige ..:rent, also, will be a
near about the site whele the insurance ufli
stood. It gives a fair idea of the cost which rail.

way companies incur when they enter the city,
if we consider what the London, Chatham, and
Dover paid to get possession of this singa ()face.
The building was IllbW and handsome, and cost,
we believe, £12,000. It is stated that the rail•
way had to pay for this building and or compen-
sation for removal no less than £40,000, for which
they received in return £4OO for the old materials
of the structure.
The works connected with the removal of old
Blackfriars•bridge have made no ostensible progress
since we noticed them last winter. The temporary
bridge is quite complete, and has been complete for
now nearly two months? but the public have been
deprived of its use because the contracts for re-
moving the old structure have not been signed.
It is earnestly to be desired that there may soon be
an end to the delays on this account, and that the
public may not only obtain the improved accommo-
dation of the temporary bridge, but may be relieved
as soon as possible from the risk which retaining
the old structure as a thoroughfare now entails on
all who use it. There is no denying the feet that
old Blackfriars-bridge is very unsafe, and liable to
become imminently dangerous at any moment. The
temporary bridge is and iias been ready for traffic
for some time past, so that there now seem scarcely
more than routine excuses for keeping it shut and
he old bridge open.

Tulloch, K.C.8., who died at Winchester on Mon.
day morning after a short illness. The gallant offi-
cer had only just left town to see a newly pm chased
property in I),,rsetshire. The late Sir A. Tulloch
was educated at Eainburgh, and afterwards went
to the Military College at Sandhurst, where he ob-
tained the highest honours in the senior depart-
ment. He entered the army as ensign in the 45th
Regiment in 1826. The late General occupied seve-
ral important administrative offices in the War De-
partment. For some time he was in charge of the
statistical branch of the War-office, and was latterly
Assistant Military Superintendent of Pensioners.
He obtained the honour of Knight Commander of
the Bath for his important civil services as commis-
sioner, in conjunction with Sir John M.Neill, G.C.8.,
in the inquiry sent out to the Crimea by the Go
vernment in 1855 on the management of the British
army during the campaign in the East. Their joint
report is generally considered due to Sir Alex. Tul-
loch, and as was afterwards declared in Parliament,
"he was it faithful exposer of the errors which
then brought our military organisation into dis-
repute." It is universally acknowledged that the
deceased General wag a valuable public servant.
His commissions bore date as follows :—Ensign,
April 9, 1826 ; Lieutenant, November, 30, 1827 ;
Captain, March 12, 1838; Major, March 29, 1839;
Lieutenant-Colonel, May 31, 1844 ; Colonel June
20, 1854; and Major-General, September 9, 1859.

THE PORTSDOWN FORTS.

Three hundred men from the 2d battalion of the
2d .:.410Yais, stetioned at Portsmouth, have encamped
on Por:.4down-hill, where they will be employed,
under the din?ction of the Royal Engineer officers
superintending the construction of the forts, in
removing the trees and
levelling the ground am.:
hedgerows from the northern slope of the hill in
the immediate front of the line of ;arts now rising
along the hill's crest. By this measure the north
side of Portsdown, which is nearly seven miles in
extent, will be converted into one immense glacis,
to the forts ranged along its top, open to the sweep
ing fire from their guns from end to end, and bare
of cover for a foe.
In The Sun of Sept. 4, 1863, under the head of
" The Fortifications of Portsmouth," was given a
general description of the line of works which are
being created along the crest of Portsdown—the
base of the great pentangular plan of defence which
is rising up and encircling Portsmouth, its harbour,
shipping, dockyard, and arsenal—and it will, there-
fore, render any further notice of them at the pre-
sent time, perhaps, the more clear and interesting
to the general reader if one of those works is
selected as an illustration of the progress which has
been made in their construction, and also of the
kind of works they will be when completed.
The Portsdown forts, with the exception of the
two central forts, vary in their designs according
to the position they hold. Thus the western end
of Portsdown is held by Fort Wallington, a very
extensive work, intended to mount 56 guns on its
terre-plein, exclusive of guns in an advanced
work, and of guns in caponnieres and mortars in
batteries in rear of the caponnieres in the ditches.
The latter aro 21 feet in width at the base, and
50 feet at the counterscarp. The eastern end of
the hill is held by Fort Purbrook and its two
outworks, Farlington and Crookhorn, and will
mount a total of 55 guns on the terre-plein, exclu-
sive of guns and mortars in the fosse. Three other
works—Widley, Southwick, and Nelson—occupy
positions along the intervening space between the
eastern and western works just alluded to. Nelson
stands nearest to Fort Wallington, and differs from
the central works of Southwick and Widley in hav-
ing its face constructed at an acute instead of an
obtuse angle. It will mount 30 guns on its terre-
piein, and will, like the others, have its guns in ca-
ponnieres and mortar batteries in its fosse or ditch.
Widley and Southwick occupy the central position
of the line, are alike in design and extent, and stand
nearest in position to Portsmouth dockyard and ar-
senal. Widley, the easternmost of the two, indeed,
commands the high road which leads from the main-
land to the only entrance to the island of Portsea,
which contains Portsmouth and all its belongings,
which these vast fortifications are intended to assist
in protecting ; and for this reason we will select
Fort Widley for our present illustration, and ap.
preach it from the north—that is, from inland, as an
enemy would approach it after having effected a
landing on some other part of the coast with the in-
tention of afterwards advancing upon Portsmouth.
I Approaching Portsdown, therefore, in this manner
frota the north, and crossing the valley at its base
between the pillages of Southwick and Purbrook,
Portsdoecn towers upwards to a height of upwards
of 400 ft above high-water mark immediately in
front, with the huge, hammocklike appearance cap-
ping the bill at ;About its centre, and other ham-
mocklike appearances right and left along the bill,
showing the position of the other forts. From the
valley the hill looks like one monster fortification,
the several forts forming the bastions, and the hill's
crest and slope the connecting curtains and cover-
ing glacis, &e. Ascending the hili'e slope the reader I
would, after some. little fatigue, stand upon the edge
of the foam or counterscarp of the dry h'oat which
surrounds Fort Widley. It is cut dov."11 into
the chalk 35ft. and 50ft. in width, the counterscarp
and escarp—i.e., outer and inner walls of the moat
being vertical, the counterscarp being merely the
unsupported chalk cutting, but the escarp being a
composite wall, to which it will be necessary to refer
again presently. At each angle of the escarp wall a
bombproof caponniere stands out into the ditch from
the fort (the counterscarp in front of each caponniere
being nut into a bay to admit of this) and sweeps the
line of moat with fire from rifle and howitzer. The
moat which surrounds the fort is thus commanded
by the caponnieres at each angle of the work, inde-
pendent of any aid from its defenders from its ram-
parts, excepting that additional assistance may be
given to the defenders in the caponnieres by a rifle
from the top of the escarp. Descending from the
counterscarp into the moat it will be found that a
considerable portion of both escarp and counterscarp
walls is lying in the moat, the chalk of the counter-
scarp having fallen from the natural effects of the
weather, and the composite wall of the escarp from
its weakness and inability to support the immense
pressure of the ramp behind it. It is built up of
segmental brick arches with 18ft. bays and 3ft.
brick piers, filled in with 18in. of flint onwards, 27in.
of chalk masonry in the core, and 9in. of brick on
the inside, giving a total thickness of 4ft. 6in. At
the angles of the wall it is very weakly designed,
and large masses have fallen bodily into the moat.
At other parts the chalk where it has appeared solid
has been allowed to form part of the lower portion
of the wall, thesbrickwork and composite wall com.
rnencing about a third of the way up the escarp. In
every instance of this kind the chalk is peeling off
in large flakes, and the composite wall must be con-
tinued to the level of the bottom of the moat, or it
i:must fall. Leaving the moat, however, with its
vertical walls and bombproof caponnieres, each of
the latter a complete little fortress in itself, the
reader can now ascend the 35ft. of escarp wall,
and stepping down inside the work from the coping
stone of the wall will find himself on a narrow
raised pathway that runs round the inside of the
escarp, and on which the defenders of the work
wcold stand when opening a rifle fire over the wall
either on an enemy on the glacis outside the
fort, or attempting to force the moat. A step lower down
again and the reader would stand on the chemin de ronde,
a pathway that goes entirely round the work, but outside
the rampart, below the line of embrasures considerably, and
eronde from
covered from observation from the outside of the fort by the
top of the escarp wall. At each angle there are loop-holed
brick
galleries,e and
face whichof thethe
rampartdef endor defenders
if couldthe escarpsweep w
thee
chagrin
being carded by an enemy. Looking over the escarp at each
ds
acanpgolenntoiewraeritathe themeosaot, erpthmereeseiwveillhtbieokseetoon bheeeotwveerengreenacithe
platforms. 'These are intended for mortar batteries for
the especial benefit of any enemy
who may obtain posses-
sion of any part of the ground or valley in front of the posi-
tion. From the chemin de ronde the grass-covered rampart
andrt i s 3tfot . above 3
stretches upwards at the usual angle of inclination, and,
this surmounted, the interior of the fort is gained. The
pthaer?eerre p
lev
plain
n 35
-
o f the
4ft. f, o
the 342 ft.
of the
parapet high-water
62 ft.at
,
its right shoulder, and 364 ft at its left. The fort is, like
all the others on tha hill, of exceedingly simple trace
twshape,
with of prodigious strength. It is of horseshoe i
with obtuse-angled faces, and with the base line of i
,lure alutting upan a military road, which extends as a
base line throughout the position and connects the forts

with each other.. The rampart has blind embrasures, ex-
cept the central one, and has platforms laid on the terre-
plein for 21 guns. The mortar batteries will each mount
five or 13• inch and the caponnieres in the moat will
mount 16 howitzers, besides having ample loopholed space
for rifle fire. The rampart at its right and left extremities
rests upon bomb-proof casements for troops or staff-
quarters ; but the gorge of the work is not yet closed, the
precise manner in which this will be dons not having yet
been decided. It was originally intended to close the gorge
of each of the Portsdown forts with iron-casen keeps,
but the absurdity of carrying out such a scheme on a hill
of chalk condemned it, and it is believed to be the inten-
tion now to close each gorge with a barrack for the accom-
modation of the garrison. As digging wells for a water
supply would be a difficult operation on Portsdown, each
fort contains within the precincts of its parade a large tank,
into which water will be pumped from the valley in front
near Southwick. In the centre of the fort parade is a circu-
lar stone staircase, which, descending 40ft. through the
chalk, leads to the main magazine, which is 50ft. in length,
17ft. in height, and 293. bin, wide. It is built up of six
courses of brick, every alternate course being of hollow
bricks, and is surrounded externally by a 2 ft. air space.
From this magazine sunken galleries, varying from 200 ft.
to 400 ft. in length, and closed by iron gates, lead to the
mortar batteries and the caponnieres in the moat. The
fort underground, in fact, with its circular staircase, maga-
zine, sunken galleries, and massive caponnieres, is equal in
interest with the fort abova ground, and would, perhaps,
be the more interesting of the two to the casual visitor.
We have noticed several errors in the construction of
the fort, but they are solely errors of design, and it is but
simple justice to say that the work of the contractor appears
to have been well and faithfully performed.

New Town-hall at Tiverton,