The Sun.
London, England, 1859-09-07 00:00:00

was constructed within this workable water, and
on its completion the pumps were set to work. The
other form of dam was the ordinary cribbing of the
country ; and owing to the rapidity of the stream
unusual care and tact had to be observed in its con-
struction. It was commenced with some prelimi-
nary cribbing, if we may use the word, 20 wide and
100 long, constructed in approximate position as to
the site of the piers and placed transversely to the
stream above the site of the bridge. -
The comparison between these two classes of
dams may thus be made :—The floating dam may
be used several times, indeed one has been used four
times, and it admits of the masonry being completed
in one season, and, -what is more, 'early in the sea-
son, and it has been found to answer best in deep
water. Its disadvantage is that it could not be made
sufficiently strong to resist the shove of the ice in
the winter ; hence it had to be removed before the
severe weather came. Consequently, when the
period arrived to construct the tube, the side of the
pier was naked, and there was no point from whence
the scaffolding to support the tube truss could start.
With the coffer dam this foundation existed, and
hence it was necessary to frame one centre scaffold-
ing only, whereas with the floating damsthree such
constructions were necessary, viz., the centre frame,
and the scaffold foundation at the side of each pier.
Nor was this consideration an unimportant one, for
such foundation was obtained by sinking scows and
driving piles around them to keep them in position.
Otherwise the operations were identical. From
either dam framing was carried up above the height
of the pier, and on the capping pieces was run a
railway, to admit the passage of a travelling ma-
chine, which, mounted with a crab, admitted a
contrary passage on itself. hence stones of
twenty tons were moved into position as easily
as a pound weight is thrown into a scale.
On the platform of the dam were constructed sheds
to cover the steam engine, the blacksmiths' shop, the
store-room, and carpenters' shop ; and thus the scene
was presented of these isolated areas of an acre and
a quarter dotted along the river, busy with life and
animation, and showing the work in its various
stages. The dam perfected, the staging constructed,
the travelling machine in position, stone delivered
ready for the mason to lay, the anxious moment
commenced—that of pumping out the water and get-
ting in the foundation. Not that the labour was
great in removing the water, but that the applica-
tion of the test, to show the dams were water-tight
and if the water would not force its way up from
below, naturally created anxiety. Nothing could be
better than the pumps used. They were worked
centrifugally, and threw 800 gallons a minute, pass-
ing up stones six inches square—the diameter of the
pipe—and it was, moreover, one of those portable
affairs that a man could take on his shoulder and
move from one place to the other. It was calculated
that these pumps lowered the area of the dam at
the rate of two feet an hour. Therefore, in eight
or ten hours the dam was empty.
MASONRY.
Three millions of cubic feet of masonry in the Vic-
toria Bridge ! That is to say, if turned into lineal
measure, it would reach 510 miles, or as a solid
would form a pyramid 215 feet high, having a base
of 215 feet square. These figures will give some idea
of the solidity of the structure, and the warrant that
exists for its endurance for all time. The stone itself
is mostly quarried from Point Claire, and. forms the
first in the series of lower silurian, and is known by
the geological term of chazy, resting immediately
on the calciferous sand rock and the Potsdam sand-
stone. At Point Claire very extensive quarries have
been in operation since 1853, and the engineer stu-
dent will be well repaid by visiting them, for stones
are taken out in as large masses as in any quarry
in the world. We see the proof of this fact in the
dimensions of the piers—the courses being 3 feet 10
inches and 3 feet to 2 feet 6 inches to above water
level, and thence verging into a course 18 inches
under the plates, being in length from 7 to 12 feet.
One course of ashlar of 3 feet 10 inches was exa-
mined by the writer; the perimeter of the pier at
this point measured 200 feet. It consists of 32 stones,
the lightest of these weighing 7 tons, the heaviest
17 ; the average weight of the whole was 102 tons.
Such work may indeed be teiied Cyclopean.
TUBES. _ .

Each tube covers two openings—that is to say,
it is fixed in position in the centre, and is free to
expand or contract on the adjoining two piers.
They are 16 inches by 19 inches at the ends, but
they gradually increase to t4e centre, at which
point they are 16 feet by 21 feet 8 inches. The
length will accordingly be—

Feet
On centre pier
Two openings, each of 242 min. .. .
Resting on east pier
Resting on west pier 8

Total • 516
The expansion rollers are seven in number, in
each set of 6 inches diameter is a cast iron frame
rolling on planed bed plates • the rollers themselves
being turned and the .bed plated, they run as
smoothly as on glass. The weight of each tube,
with all its appurtenances of 516 feet, is about 644
tons ; that is to say, for each opening 322 tons.
The construction of this character of work is now so
well known that much allusion is not necessary.

PRESENT CONDITIJN OF WORK.
The abutments and piers are all complete, with
the exception of Nos. 14 and 15, which are built
6 feet above water level, and No. 11 pier, which was
purposely left untouched in order to leave one
channel open for rafts, the waterway being nar-
rowed between the piers already constructed by the
cofferdams. The two former will be finished in 20
days after the working season commenees, the latter
by beginning of September.
Of the tubes 16 of the 25 are fixed and finished
in position. The centre span is completed.
And on or about the Ist day of October, in the
year of our Lord 1859, this wondrous work will be in
full play, bearing the tread of the mighty steam
steed, conveying man and all the materials of man's
varied business on this great continent fro.ii the
ocean's shore to the fresh water seas of the remote
West. It is expected that the Leviathan steamer,
bettring thousands from the Old World, will have
arrived at Portland not long after this great cele-
bration, and thus will Americans be called upon
at one and the same time to render hearty homage
(as we are sure they will) to the mechanical genius
of their brethren of the English dominions, as
shown so wondrously in these joint works.