Vermont watchman and State journal. [volume] (Montpelier, Vt.) 1836-1883, 1849-12-13

IL
almost entirely borne by the upper and low
er surfaces former having to resist
compression and the latter diStension. TO
make beam, therefore, which should, with
the least weight Of its own, resist the great
est pressure, the material TO be used should
be accumulated at the top and bottom where
the strain is greatest, or in other words,
the middle of the beam, whether of wood
or iron, should be bored om.
Now if Mr.. Stephenson had extended a
cross the Straits solid beam of iron, capa-
bic Of sustaining the. required weight, it
would have been crushed by lis oDn weight.
He resolved, therefore, to bore out the mid
die of (which would only increase the
weight without adding to its strength in
other terms, he determined to build a hol-
low beam. After further experiments upon
the kind of material best adapted to the U.s.
cs respectively. of the upper and lower sides,
it was ascertalned that cast ir0n can resist
per square inch
Compression of from 35 to 40 tons.
Extension 3to 7
Wrought iran can resist per square inch
Compression of from IL to I3 tons.
Extension q" l6 to IL
Mr.. Stephenson finally determined to use
acrougM iron only in the construction of his
bridge, and that the relative strength in the
top aud bottom should be as 5 to A. Max
ing further experiments in regard to the form
of the tube, he found that their relative
strength was as follows, Crcuiar l3;-
EMpticai 10 -Rcctangulor 2l. He re-
solved therefore to make the tube rectangu-
lar. Further experiments were made to de-
tcrmine the strength necessary for the sides
Of the tube, the best form for riyets the
proper shape and size ofthe plates, &c. &c.
1t was decided furthermore, to make the
upper and lower side Of the tube, of plates
laid foot or two apart, the inclnded hol-
low space being subdivided by small vert-
cal plates into rectangular passages or Aucs,
extending along the top and bottom Of the
tube.
In regard TO the weight to be sustained,
it was found that common Railway train
weighs about a ton per iOot-the length of
the longest tube was to be 400 ieet,-so
that the weight which it would have to bear
would be iGJ tons over the whole surface,
equivalent to ? 30 tons at the centre. In or
der to assure the public of the safety of the
bridge, Mr.. Stephenson resolved to make it
capable Of sustaining 1900 tons over its
whole surface, or 1000 tons in the centre
about nine times greater than the amount of
strength necessarily required. The maxi
mum lateral pressure of the wind upon the
/, bridge was found to be 277 tons, or 1873 at
the centre: Mr. Stephenson planned the
: bridge SO as TO be able to resist fee times
this pressure.
These preliminary calculations having
been made, and and approved by the Com
pany, MIR. Stephenson set about the con-
struction of the bridge. 1'he ground was
: cleared, houses were butt for the workmen,
church aud schoolhouse were erected and
provided with clergyman and teacher, and
soon upon the spot which had been covered
: with dense and savage forest, grew up a
: busy village which resounded fom morning
: till night with the dia Of hammers, anylls
and engines of every kind.
The Quarterly gives very detailed and
: highly interesting description of every step
IN the process Of this immense fabrication,
the size, shape and manufacture of the
plates he manner constructing, placing
and driving the rlvets, &c, &c.,-all o.
which IS exceedingly curious and entertain
;. ing, For thus, however, we must refer our
readers to the article itself, as our space
will not permit any transfer of it TO our COL
umns. In due time the work was DONE
The four ends Of the two tubes were con-
structcd eli the spot, and in the position
which they were TO occupy The four lar
ger central portions were built upon the
, edge Of the stream, at high water mark, up
on wooden platforms, from which they were
to be iloaed on pontoons to the bases of
the towers on which they were finally to
, rest.
: The next step was the floating ofthe first
tube finished, an immense iron structure
Az feet in length, ID high, and 80 wide
and of this the Quarterly gives a most ami
mated aud picturesque description. Thou
: sands and tens of thousands of spectators
were assembled to witness the operation
The central tower rising from the middle of
the stream to height OF $50 feet, contain
ed las, 625 cubic feet of marble for the ex-
, terror, IA, 625 of sandstone for the interior
and 3S7 tons ofcast iron beams and Orders
) worked in TO give strength and security to
the mass The only way of ascending it
was by ladder. -Four colossal statues Of
: lions c0uchant, each IL feet high and 25 feet
long, and weighing 30 tons, terminate the
land abutmenls ON both sides. The tube
I had been made circular on the bottom, the
middle being nine inches higher than the
ends, in order that when the supports
should be removed and the tube allowed to
rest on its two ends alone, it might lie
Strengthened by its own weight, which it was.
: The earth had been excavaed under the
two ends, until on either side there was
found dock sufficient to admit four pom
toons, each 90 feet long, % wide, and Il
, deep. These pontoons were furnished with
valves, so that the water could be let in, or
:. kept out, at pleasure. Capstans had been
provided to haul these pontoons into their
places, when they should have received their
load
Everything being ready, the valves were
closed, and the pontoons rose with the tide
until their Atantean shoulders were placed
, beneath the stupendous tube which they
were to lift. In Il few moments the vast
structure was seen to have been lifted from
its bed the hawsers which had kept it in
its place were cut by axes, aud the whole
moved silently, slowly, and majestically into
the water. The capstans were then put in