Evening star., 1901-05-04
At the Approach ola Boat They Split
in Two.
EACH END RISES HIGH IN THE AIR
Easy of Operation and Save Lots
of Time.
HOW THEY ARE Blu IL

Written for The Evening Star.
In medieval times the feudal lord be-
sieeed in his battlemented castle shut off
communication with the outside world by
simply drawing up the bridge spanning
the moat surrounding the fortress, very
much as a hinged trapdOOr might be raised
The dawn of the new century finds TINS
same principle, with notifications and I'M
provements utilized in Americas busiest
inland city in order that the flow OF Its
traffic by land and water might be less
seriously interrupted than by the cllmber-
some drawbridges of the old type, slowly
swinging on a pivot.
Some time ago an elevated railroad found
its entrance to the business center or thi-
cago blocked by the necessity of providing
a form of bridge which would permit the
heavy traffic over its four tracks to cross
the Chicago river without seriously inter
fsring with the commerce of this crowded
stream up and down which thousands OF
vessels pass every month IN the season
of navigation. The perpleXing problem was
submitted to a number OF prominent en-
gineers and finally one of them, MI VIII
liam Scherzer. hit upon the idea OF the
rolling lift bridge. the introduction OF
which has marked new era In the prog
reSS of movable bridges.
What They Look Like.
A man interested in the invention has
compared one Of these new bridges to a
pair of giraffes standing on opposite banks
of a stream, their heads meeting In the
center Of the brook they drink, which,
when startled suddenly rear their necks
perpendicularly on either side of the water
way. The simile aptly illustrates the work
ings of these remarkable aids to commerce.
In appearance rolling lift bridge Is very
similar to eny other steel suspension struc-
ture of the same class, broad ana low ana
of comparatively short span The roiler
bridge however, is cut in two Squarely III
the center and when a boat desires to
pass. instead of drawing aside or swinging
around in the middle of the stream after
the fashion Of the ordinary draWprloge'
each half Of the structure is quickly drawn
by an invisible force to an upright posi-
tion on the bank of the river.
In order to facilitate the sudden rearing
In the air of these great masses Of iron and
steel the ends of the bridge resting on the
river banks are rounded off much after the
fashion of the rockers of rocking horse
Electrical power is utilized, but SurprlS-
ingly small amount of the magic current is
used, the moving spans being so perfectly
counterbalanced that they rock or roll vir-
tually without friction in opening and clos
ing.
The time-saving element is one Of the
chief advantages of this new invention. The
movable spans even of the largest rolling
lift bridges respond and acquire momentum
SO rapidly that the current is usually turn
ed into the motors for less than twenty
seconds for complete operation of opening
and closing the bridge.
They Are Kept Busy.
One man can operate this type of bridge.
A majority of the rolling lift bridges in Chi
cago have movable spans ranging from 100
to 200 feet in aggregate length and wide
enough for several teams abreast. There
are also now in use rolling lift bridges
crossed by two. four and even six railroad
tracks. over some of these more than a
thousand trains pass every day in the year.
The Rush street bridge is probably the
most active bridge in the world. A record
recently kept for 2J9 consecutive days
showed that in that time the bridge was
opened 10.iG0 times. giving passage to 70
SCI vessels In other words. the structure