The Davenport gazette. [volume] (Davenport, Scott Co., Iowa) 1841-185?, 1850-01-17
THE MAGIC BRIDGE.

THE MAGIC BRIDGE.
We have examined with much interest
and attention, the model, or rather the spe-
cimen Of bridge, erected 10 the Arcade by
Mr.. Remington, Of Alabama, who is the in.
ventor OF it. The more We have studied it
the less we acknowledge we are able to un-
derstaud its principle, or rnlher its mystic.
ry, and we have nothing to depend upon
to prove that principle (prelty good depen-
dence, howeyer,) but stubborn facts, and
the evidence OF our senses.
II The bridge extends across the wide room
Of the Arcade, distance Of ninety feet
and is supported only at either end. Its
whole strength consists Of only four sleep
ers, or rather slips OF wood, two aud halt
inches square at the abutment end, and
gradually diminishing to the centre, where
they are only seren eights OF an inch
square.
1 In order to form footway on them they
arc crossed diagonally with small slabs Of
wood, at close intervals, each s,hs ofan inch
thick, Al inchs wide, and about Q feet long.
The strength of the bridge, however, con-
sists only ofthe above four pieces Of wood
sibs Of an inch square.
i The first aud obvious impression is, that
these nre insufficient 10 sustain their own
weight for such span, as we believe It Is
asccrtained that piece ofyellow pine one
inch square and % feet long, will break by
its own weight, if supported merely at eth
er end. Yet Notwithstanding these small
and apparently frail materials, MIR. r. as
sures ms It will bear the weight Of seren
tons placed on the centre! We ourselves,
have seen ten men standing on the centre
Of this light and airy structure, without ha-
wing the least effect upon it, aud we under
stand seventeen have been on It at one
time.
i This result is tho more extraordinary,
as wood imployed and placed in this man
ner, il has been ascertained, will sustain a
greater weight than if placed in a perpen-
dcnlar position, and the weight suspended
at the lower end. Pine wood an inch
square, attached at the upper end, and
suspended perpendicularly, will sustain a
weight of 1910 pounds before it will separ-
ate, but here we see four pieces, each only
. seyen-eighihs Of an inch square, placed in a
horizontal position, sustain a weight Of a.
600 pounds, or $500 pounds each, without
, fracturing!
The line of the bridge as it starts from
the abutments, rises for short distance
and forms what is called the parabolic curve
and then gradually sinks to the center, in a
catenary curve, the greatest depression
, however. being only one-serentieM Of the
, cord line ofthis curve, and the depression
, Of the center being still aborc the com
mencemenf Of this bridge at either end
The secret Of the strength Of the bridge ap,
) pears to be in the parabo!ic curve at either
end, as without it, and snpposing the bridge
to swing from each end in one curve, in
the same manner as rope, the msterial
, would break by its own weight, in much
less span than the present model. Why,
, or wherefore this should be the case, is, We
, acknowledge, "past our philosophy to find
! out"
, In England various bridges of this kind
have been erected, with materials in no in
stance, exceeding six pieces oftimber. not
more than two and half inches square ia
the center, with a width of eighteen feet for
the structure, afording passage for the
. heaviest loaded wagons, even in continued
, trains, besides having the whole curative
filled up with gravel on the platform ofthe
+ bridge, SO as to. make perfectly level road
, Mr. Remington states that bridge one
mile or even longer, can be formed on this
plan with no larger materials than the
above, say six string pieces, each four and
halfinches square at the abntments. and
{ diminishing to two and half inches at the
centre, and that bridge even of that length,
would bear any transportable weight that
can be placed upon il, besides being per-
fectly steady, and free from vibration; par
| ticularly if loaded on the platform through
it's whole length, with a solid, well rolled
gravel road.
i A prominent advantage of this kind OF
bridge is its cheapness, particularly where
there is great span, when it can be con
structed for cost probably not exceeding
the tenth Of one on any other plan. An
other advantage is, that il can be erected
in situations where other kinds Of bridges
would be inpracticab!e; and third advan-
tage, that the span can be greatly extended
beyond that Of any other kind oil wooden
} bridge.
/ We strongly recommend It for adoption
in the United Stntes. The model at the
Arcade is well worth Of inspection.-NO.
Bulletin.
WErTING BRIcK.--A wall twelve inches
thick, built Of good mortar, with brick well
soaked, is stronger, in every respect, than
one sixteen inches thick built dry.