The Rock Island Argus. (Rock Island, Ill.) 1877-1885, 1883-05-25

concluded to use only granite and briek s-.e
in the world The foundations were built by
the aid of eaissons, which were sEink like hugs
wooden 4 living bells. tbs. eaissons tops being
| and Bolts aggregating 250 tons in weight, and
their sides tapering from feet down to .
inches thick, and these We're sunk by MASSIVE
stones and their own weight TO the exact
| point intended for them. In May, 1870, the
berth near the Fulton street ferry
slip, and granite blocks of tons each
laid upon it until the middle of July. when
sorkmen began to excavate beneath it. After
depth Of i515 feet was reached, the. caisson
left the work being finished In March, 1871
On the New York side the caissons sunk
TO solid bed of rock, at depth of g feet
Other eaissoIls were sank IN October, ISL and
May, 1872. In the meantime, Mr. John A
Roebling had died from lock-iaw eansed by
the Crushing Of his foot and the rest Of the
work was conducted by his son, Washington
A. vkoebllng. who has directed the opera
tione from sick-roon, Having con-
| tracted the caisson disease III 1871.
Ihis same calsson disease is the result of Iiy-
ing under atmospheric pressure greatly above
that TO which the human system is normally
adapted The blood ls driven III from the ex-
terror aud soft parts of the body to the central
organs, especially the brain and spinal cord
On emerging into the open air violent neural
gie pains and sometimes paralysis follow DIR
Andrew III. Smith, surgeon TO tho bridge coTd
pany, reported no eases of the caisson dis
ease of which three were presently and prob
ably more finally fatal
The construction of this gigantic cobweb for
| travel has furnished an epi5odesof engineering
the magnitude of which few appreciate.
The towers are 276 feet inches in height.
The cables are anchored inland at distance of
g3eAteet back from the towers on each side.
The anchorages are trIumps of stone masonry,
ll9 by l33 feet at the base and rising to eie-
yation OF ninety feet above high water mark
Weighing about 60, 900 tons each they are oil
course capable OF resisting an enormous strain
from the cables A stranger viewing the tow
for the first time ma turallv asks, How
was 1t possible to obtain proper foundation
for such structures 50 near the water?"
The cables sweep gracefully over the top of
towers 20 feet in height The bridge floor,
which the cables sustain, is an immense steel
framework consisting of two systems of z rd-
efs at right angles to each other The main
Orders, supporting the fioor proper, ere grace
fnl trIlsses thirty three inches deep placed
seven feet SIX inches apart To these at
taehed four steel rope Buspenders from the
cables. Parallel and longitudinal trusses,
strength IN every direction. AT the towers the
framework Is firmly anchored The weight OF
the central Fpan of the entire suspended
structure ID g 740 tons. 1t is estimated chat at
no time will this weight be increased by
cars, vehicles and passengers more than $50
tons, giving a total maximum weight of s, 100
tons. OF this enormous weight o. go tons
sustained by the cables and ], I9o tons by tho
suspensory stays of steel wire ropes divefging
from the tops of the towers to points about
fifteen feet apart along the bottom of four OF
the vertical trusses. These stays extend out
from the towers 400feet They form import
ant auxiliaries to the cables. The central ave-
nue. of the bridge is to be used as footway.
Its width is nineteen feet, and it is elevated
above the avenues on the sides some ten feet
The side avenues are occupied by cars NOV
ing from end to end by means OF an endless
wire rope operated by q stationary engine
The cables suspended from the great towers
are fifteen and three-quaftar inches thick In
each cable there are 5000 wires, the whole
mass being suhdigided into skeins strands
OF us wires each, and each skein IS a continu-
GUS wire nearly ,0oo,o feet in length The
first man to cross from towef to tower was Il.
r. Harrington, the master mechanic of the
terprlse who made the trip August D. 1876
Then the detail of the work went on, each day
adding to the humber of wires from tower 10
tower, until finally light foot-br1dse
across, and all who desired could walk from
one anchorage to the other over the tops of the
towers and across the river. Then the cradles,
ten in number, were got in position, that the
men engaged III the cable-making could regu-
late the wires, matter OF no small difficulty,
since the atmospheric effects of the and
wind were such that frequently the cables
varied much as half a foot in height in the
course OF day. The reflections were, how
ever, all overcome, and the last wire was run
across Oct Is, 1873
The total length of the bridge is ), $50 feet !
The length of the river span Is l $780,. feet and
at the centre it will be 135 feet above hugh
water mark IN summer and I3S feet winseE,
the difference being .sed by the effect of The
heat and cold on the steel The wind blowing
at velocity of 100 miles hour would not
hurt the bridge. The greatest velocity of the
wlnd here is III miles an hour. The centIe of
the suspended strtIfessra - u feet higher than
the roadhays of the towers. Not 3 per
cent. OF the vessels that enter this port would
have to strike their topmasts in passing under
the bridge. From anchorage to anchorage the
bridge rs $3.50 feet long, aud the total weight
of the suspended structure Is IL, $50 tons. The
CA las, Chief Engineer Roebliag says, are
strong enough to pull up the anchorages,
which weigh 60,0o0 tons each The bridge is
to be lighted by 100 electric lights.
THE ACCIDENT IN 1873
It is rather remarkable that from first to
last no one has ever fallen from the dizzy
height of the main.span INTO tie water beneath
Besides the fire in the Brooklyn caisson, which
cost no lives, and the fall of the. derrick ON the
Brooklyn tower, which had more serious re
suits, there haa been one great accident ouly,
bat the ina gina ton can scarcely picture any
thing more dreadful. On June - fo9S, one of
the great stranda broke loase from the New
York anchorage CafTylfg with it the %shoe" and
its ponderous attachments As the end swept
from the anchorage 1t dashed off several af
the men at work, and then, with a frightfui
leap, grazing the houses and peopled streets
below, it landed for instant in the bridge
yard close under the New York tower The
great weight midstream whiEzed 1t over the
tower with frightful IA | increasing Tapldity,
and the whole strand plunged madly into the
river, narrowly missing the ferryboats that
ply crowded with human freight, below tile
iie of the bridge.