The Sun.
London, England, 1849-10-16 00:00:00

THE BRITANNIA TUBULAR BRIDGE.
MENAI STRAITS, MONDAY AFTERNOON.—This
afternoon the final lift of the Britannia tube took
place at three o'clock, the permanent level of 100 feet
above high water mark having been successfully
attained on Saturday, when its ultimate eleva ion
was enthusiastically hailed from all parts of the works
with cheers and a succession of salutes. This addi-
tional bolt of three feet had to be made, and was in
dispeasably important to enable the engineers engaged
in the oleration to join the great tube on to the end,
or land tubes, before laying it down on its permanent
bed plates and rollers, which will have to be placed
beneath it. This process of adjustment will occupy
three weeks.
It will be matter of surprise, however, to many to
be made acquainted with the fact, that in the success-
ful raising of the one tube to its permanent level one.
eighth part only of these colossal labours was accom-
pliihed. There are three similar lengths of tube to
be floated and lifted, besides four of what are called
land tubes, before the stupendous fabric is completed.
The cm set of tubes, giving a total length of
1,849 feet, will only form the passage for one line of
rails across the Straits, and alongside of these
another set of tubes, exactly similar and parallel, will
have to be raised to furnish a double line of rails for
the up and down line. The great object at present
in view is to get one completed, which, until the
second set is ready, will be used both for the up and
down trains, the passage of which will be regulated
accordingly. To show what has yet to be done, as
well as to illustrate the arduousness of the prospective
operations, a statement of the approximate dimen-
sions, and of the gross amount of material to be em-
ployed in the entire fabric, will be interesting. The
total length of these continuous tubes will be 1,849
feet; the total length of the tubes for both lines of
railway, 3,698 feet; the greatest span in the clear,
460 feet ; the height of the tubes in the middle, 30
feet; height at intermediate piers, 27 feet; height at
each end, 23 feet; extreme width 14 feet 8 inches.
The number of rivets in the entire bridge is 1,764,000 ;
the amount of iron calculated to be used is in the first
land tube, 274 feet long, 450 tons of plates ; in the
other three, of the same length, 1,350 tons; in the
first tube of 472 feet long, 965 tons of plates ; in the
three others of the same length, 2,895 tons of
plates ; making a total, with pier tubes, of 5,778
tons. The total computed weight of angle iron to be
employed in them is 1,240 tons, of T iron 856
tons, of rivet iron 656 tons, of cast-iron in the
frames and beams 2,000 tons ; making a total dead
weight of 10,570 tons. The total length of the tubes,
if placed in a line, would be about three-fifths of a
mile. The strength of this great rigid structure con-
sists in what is called the cellular system, found so
effective in resisting lateral and vertical pressure.
The plan, as in the tube now raised, consists of a series
of cells or pipes at the top and bottom of the tube,
ranged in hollow compartments, covered above and
below by iron plates rivetted together, and having a
parallel direction to the long axis of the tubes. These
cells are sufficiently large to admit of the entrance of
a man for the purpose of being cleaned and repaired.
It was originally proposed to have a double tier of
these cells at the top, more effectually to resist the
crushing force, but the construction of a single tier
was subsequently resolved on as sufficient. These
cells have the effect of placing the resistances of com-
pression and expansion nearly in equilibrium with
each other. The utmost tenacity and stiffness is ob-
tained, with the least possible weight of material, and
it is believed that a tube of 1,000 feet span might be
constructed with safety upon this cellular system of
rigidity and strength. Trains have passed through
the smaller scale of tube at Conway for months,
without any injury or effect whatever. No motion
can be detected by the eye during the passage of a
train, and instrumental observations detect a deflection
of only the eighth of an inch. It has been found that
the effect of a very severe gale from the riorfit-west
on the side of the Conway tube, at an angle of about
50 degrees, produced an oscillating motion, which
being carefully measured gave a lateral deflection of
only 0.23 inch. It is found, moreover, that the
enormous weight of the tubes themselves, opposed to
the impulse of the wind, is a security against con-
tinuous oscillation. The effect temperature constantly
produced, but in no way injuriously, on these large
surfaces of iron, is remarkable. In the afternoon, the
sun shining on the top and on one side, the tube is
bent in that direction 0.96 inch, or nearly one inch.
On comparing the deflections of the morning with
those of mid-day, a decrease of 7.10 of an inch was
observable, or a rising in the middle of the tube had
taken place to that extent. The result of a change of
temperature is an increasing convexity in curvature
of the top and bottom sides, to the extent of raising
the entire tube 0.71 inch in the middle.
A large number of distinguished visitors have been
to inspect the tubes and stupendous works during the
last few weeks, amongst them their Royal Highnesses
the Duke and Duchess of Cambridge, who spent a
considerable time over the tubes, Prince George of
Cambridge, Lord Vivian, several of the nobility, and
almost every engineer in the kingdom. It is intended
by the directors of the Chester and Holyhead Railway
to give some cheap excursion trains periodically to the
Straits, to enable the middle and humbler classes to
visit these noble works of art. Two additional cylinders
have been cast for the lifting of the next tube, as a
reserve, in the event of the one in work failing. All
the preparations are complete for the floating of the
next tube, which will take place about the middle of
November. The day at present fixed on, should no
unforeseen contingency occur, for the completion of
one highway and the transit of the first train over the
Straits, is the Ist of March next.