Imperial Valley press., 1911-12-16
NATURAL BRIDGES
We Can Boast of at Least Nine
of Them In This Country.
OUR FIRST WOODEN BRIDGES.

They Were Built About 1900 In tho
Eastern and Central States, and Then
Came the Covered Structures-Few
Iron Bridges Prior to 1850.
Nature has provided this country
with at least nine natural bridges, one
in Virginia with a span of about nine
ty-three feet and about 200 feet high:
one in Alabama with span of about
seventy feet and about 130 feet high:
five in California. the largest of which
has a span of about eighty feet and is
about twenty feet high; one in Ken:
lucky with span of about seventy
feet ana about 13O feet nigh. ana one
in southern Florida of somewhat
smaller dimensions.
Bridge building in the United States
is of comparatively recent accomplish
ment. The early settlers were com
PEELED to ford the streams or cross
them on rafts or in dugouts. When
Washington crossed the Delaware with
his army there were no bridges over
that river. and history records many
instances of streams being forded with
untold hardship and the consequent
disasters and delays. Such incidents
become serious matters when. for ex-
ample, physicians are unable to reach
the sick or injured because of impass-
able fords or are compelled to expose
themselves to unnecessary danger.
Traffic conditions in general are de-
| moraliZed by unsafe bridges or cul-
vertS.
| Pontoon bridges have served tempo
rary need in many instances. but espe-
cially in warfare. Mention is made of
| their use very early in history. and one
| of the most notable occasions was
when the Persian army under Xerxes
| crossed the HelTespont on two pohtoon
bridges consisting, one Of $50 vessels
and the other of 314. These were an
chored head and stern alongside of
each other. with their keels in the di-
rection of the current.
| The Romans had wickerwork vessels
covered with hides destined to support
| the timber platform Of a bridge. These
| formed part of the train of their ar
mics throughout the history Of the en-
pire until 476 A. d.
The construction of highway bridges
in this country began to assume prac-
| teal proportions about the year 1900,
when many wooden bridges were built
in the eastern and central states by
Theodore Burr and Timothy Palmer.
The wooden lattice truss was intro
duced about 1920 by Ithiel Towne.
Many of these bridges. consisting of
planks pinned together in lattice work.
were built from this time on. and they
| became we'll known as "Iowne" or
covered" bridges. 1t is doubtful if
much attention was given to econom-
| ical design. An effort was made to
| protect the trusses from the weather
| by wooden roofs and sides in some in
stances. but very few were ever paint
ed to preserve the timber. This early
| type of bridge did service for many
years. and some are still in existence
in Indiana and elsewhere.
The first covered bridge to be built
in Tippecanoe county and one of the
! first in central Indiana was the
Brown street bridge over the Wabash
| river at Lafayette. according TO the
records on file in the office of public
roads. department of agriculture. This
old structure. that had been condemn
ed for good many years. has long
since disappeared. However, a num-
ber of covered wooden bridges that
| were built more than half century
wi n
dius of fifty miles of Indianapolis.
Few iron bridges were built in this
| country prior to 1850. and it was only
| in 1S47 that the first publication in the
| United States. discussing the rational
| design of bridge members, was issued
by Squire Whipple of Utica. N. Y.
| Wrought iron began to replace cast
iron about 1868. but steel was not used
until about ten years later. The ad-
vantage Of steel over cast or wrought
iron lies in it's greater tensile strength.
Foremost among structures repre-
senting some of the attractive as well
as substantial features in good bridge
designing of the present age may be
mentioned the Washington bridge over
the Harlem river in New York." said
the superintendent Of construction Of
bridge engineering. office Of public
roads. Washington. This bridge has
two middle arches Of steel. each SO
feet in clear span. and seven masonry
arches, each with a sixty foot span
It's total length is 2.375 feet. while
the width Of it's roadway is eighty