The Anderson intelligencer. [volume] (Anderson Court House, S.C.) 1860-1914, 1902-09-24
When Bridges Breathe.

Though to speak Of bridges breath
ing appears passing strange, never
theless, inanimatc struc. ures are never
still for memen. during the liyeloug
day.
The Britsnnia bridge, for instance,
which is 400 feet long under normal
circumstances, ia from half TO 3 inches
longer at 3p. M. than it is at II
hours later, according to the amount
of sunshine it is subjected to, which
draws it sometimes an inch upward
if the heat strikes the top of the
tube, or to one side when the sun in.
creases it's temperature literally,
though the heaviest train will only
bend it half an inch at any time. In
like manner intense cold will cause q
bridge to shrink more appreciably.
OTo show how intense the cold must
have been, we have only to point out
that Southwark bridge over the
Thames, which, however, is only
about oneninth the length of Brook
lyn bridge, Only rose in the centre to
the amount Of l4inches for SO degrees
rise in temperature. To allow for ex-
passion or construction the builder Of
the Clifton suspension bridge provid-
cd the ends of the roadway with him
gcd flaps 8 feet long, which allow Of
perfect freedom of movement; and the
makers Of the tower bridge, which is
about q inches longer in the sum-
mcr than in the winter, made simi-
lar allowance.
After the choir of Bristol Cathe-
dral was covered with sheet lead in
1851, it was discovered two years
later that, notwithstanding the fact
that the length Of the covering was
60 feet, and its depth 18s feet, it had
crawled down bodily for 10 inches,
drawing out nails from the rafters in
it's course which had been driven in
to arrest its progress. The explana-
tion Of the movement lies in the fact
that the lead naturally expanded more
freely downward than Upward when
subjected to the suns 8 heat, and that
when it contracted at night it drew
its upper edge after it. in preference
to climbing up to it.
The Eiffel tower, like the Britannia
bridge, is ever on the move, either up
ward or downward, according to the
temperature, the summit of the scw-
er, SO it is said, entailing an extra
climb Of five inches when the temper
aturc is high than in the cool of the
day, while in winter it is 8 inches
shorter than at midsummer. Even
the white marble obclisk dedicated to
Washington which was erected at a
cost Of s2GO,0O0 rears it's head $50
feet in heigth on the bank of the Po-
tomau, is not proof against the power
of the sun, and is said to increase it's
height by 2 inches and to hend slight
ly on hot day.
With regard 90 the latter movement,
q copper wire l74 feet long, carrying o
plummet suspended in q vessel of wa
ter, renders peroeptible the slight
bend Of the sheft caused By the rays
OF the sun pouring on one side only,
though the inclination Of the az :: OF
the monument amounts TO but o few
hundredths Of an inch toward the
north each day at noon throughout
the summer.
The railway line is very powerful
respirator. Probably every Answerite
has noticed the gap between each
rail-. In winter the chinck will be
over q quarter IT an inch in width,
but in summer it will be quite closed
up. During one uf the frequent civil
wars. incidental to South America one
of the belligerents conceived unique
idea of train wreckiug. During the
night he drove steel wedges tightly
into these gaps for considerable dis
tance. The heat Of the sun next day
caused the rails 90 breathe heavily,
but they could not expand lonei-
tudinally they twisted themselves
clean out Of the chairs which clamped
them to the sltrpers and th. rail u ay
was rendered completely useless for
traffic.
"A bAt,leship is over 6 inches long