Middlebury register. (Middlebury, Vt.) 1886-1937, 1889-11-15

Sir Thomas Bouch had taken in hand the
job of spanning the Firth of Forth, had
planned a huge suspension bridge and had
considerable work done on it when the Tay
disaster put an end to the project at once and
forever In the natural reaction Of horror
there was a general protest against any
bridge, and a very extensive feeling that no
safe one could be built In due time, how
ever, the question was submitted to three
eminent engineers, Messrs John Fowler, w.
II. Barlow and 7. Z. Harrison. After care
full inquiry they decided upon a cantilever Of
plan jointly devised by Mr.. Fowler and Mr.
Barker, and the bridge thus arranged for is
now rapidly nearing completion.
By glance at the annexed eugravings and
the following figures the reader will see what
enormous difficulties they had to overcome;
and but for the rocky little Isle of lnchgar-
vie, in the middle of the Firth, the new
bridge would have been an impossibility.
That island is but mere point of stone, but
it is enough. On each side of it the channel
is nearly | 200 feet wide, the water is over
POO feet deep, and yet the railway track, on
a level with the approaches on each side, is
252 feet above average tide To span such "a
chasm with a bridge sufficient to support the
heaviest trains and proof against the great
was indeed Il task for engineers. Yet all in
spectors and scientific visitors admit that
they have accomplished it.
The structure is briefly classified as Can
tlever truss double span bridge all steel, and
the largest of its kind in the world" The
material used is tested for an ultimate resist
ance of thirty tons per square inch in tension
and thirtyfour tons iii compression; it will,
therefore, sustain four times the combined
strain of a wind pressure of fifty-six pounds
to the square foot and maximum running
load of two tons to the foot or 3, 400 tons to
the span 1t might be well for the North
British Railway company to have cards
printed with engin GERS certificates to these
facts and have one handed to each passen-
ger on the line just before the train reaches the
bridge, as passengers will certainly feel the
need of such an assurance of safety If they
see the structure they are about to pass over.
The cantiever has the shape of an elon-
gated diamond, and there are four masonry
piers supporting the four gigantic legs on
which are poised the balancing arms, and
these extend out 60 feet on each side of the
base The old "parlor magic trick of stick
ing two demonstrating forks into cork to
make it balance and dance on IA string, gives
some faint idea of the necessity for such i'm
mense balancing arms. The middle can't
lever is longer than the other two, its base
being 270 feet long, while theirs are l55 feet.
The greatest height of the bridge above the
piers is $50 feet, and the ends of the cantilever
beams are still $50 feet apart SO they are
joined by lattice girders resting on the ends
of the arms. With these figures, the reader
can see the enormous size of the diamond, "
and the daring and extent to which the can't
lever principle has been carried Neverthe-
less as the extension each way is equal, the
safety is great as if it were on smaller
SCALE