The Davenport gazette. [volume] (Davenport, Scott Co., Iowa) 1841-185?, 1850-01-17
DAVENPORT SCOTT CO, IOWA. THURSDAY, JANUARY H. 1880
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 il
the less we acknowledge we are able to un.
dcrstand its principle, or ra,her its mystic.
~, and we have nothing to depend upon
to prove that principle (prcity good depen.
dence, howeyer,) but stubborn facts, and
the evidence OF our senses.
4 The bridge extends across the wide room
Of the Arcade, distance Of ninety feet
and is supported only at either end. IL
whole strength consists Of only four sleep.
ers, or rather slips Of wood, two aud hall
inches square at the abutment end, and
gradually diminishing TO the centre, where
they are only seren eights OF an inch
square.
/ In order TO form footway on them they
are crossed diagonally with small slabs ol
wood, at close intervals, each sths olan inch
thick, Al inchs wide, and about 8 feet long
The strength Of the bridge, however, con.
sists only ofthe above four pieces Of wood
| aths OF an inch square.
The first aud obvious impression is, that
these are insufficient to 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,
hive seen ten men standing on the centre
of this light and airy structure, without ha-
wing the least effect upon it, and we under
stand seventeen have been on it at one
time.
This result is the more extraordinary,
as wood imployed and placed in this man
ner, it has been ascertained, will sustain a
greater weight than if placed in a perpen-
dicnlar position, and the weight suspended
at the lower end. Pine wood an inch
square, attached at the upper end, and
suspended perpendcularly, will sustain a
weight Of lO4O pounds before it will separ
ate, but here we see four pieces, each only
). seven-eighths of an inch square, placed in a
horizontal position, sustain a weight Of a.
600 pounds, or $500 pounds each, without
frac,uring!
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-serent;eM Of the
cord line ofthis curve, and the depression
Of the center being still aborc the com
mencement 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 supposing the bridge
to swing from each end in one curve, in
the same manner as rope, the material
would break by its own weight, in much
LEES span than the present model. Why
or wherefore this should be the case, is, we
acknowledges, "past our philosophy to find
out"
4 In England various bridges of this kind
have been erected, with materials in no in
stance, exceeding six pieces oftimber. moi
more than two and half inches square in
the center, with width Of eighteen feet 70,
the structure, af1ording 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
a halfinches square at the abutments, 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 it, besides being per-
fecty steady, and free from vibration; par
iicularly if loaded on the platform through
it's whole length, with solid, we'll rolled
gravel road.
A prominent advantage Of this kind of
bridge is its cheapness, particularly where
there is a 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 it can be erected
in situations where other kinds Of bridges
would be inpraciicab!c; and third advan-
tage, that the span can be greatly extended
beyond that Of any other kind Of wooden
bridge.
We strongly recommend it for adoption
in the United States. The model at the
Arcade is well worth Of inspection. O..
Bulletin.
WErTING BRICK.--A wall twelve inches
thick, built Of good mortar, with brick well
soaked, is stronger, in every respect, thai u
one sixteen inches thick built dry.