The Mount Holly news. [volume] (Mount Holly, Burlington Co., N.J.) 1891-1942, 1913-02-25
HEAT OF The sun
Old Sol Has a Strong Pull at the
Capitol In Washington.
SWAPS THE MAMMOTH DOME.
On Hot Day His Torrid Rays VIII
Drag the Massive Iron Structure
Way Out of Piumb--Tu the Same
Trick With Washinaton Monument.

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Drag the Massive Iron Structure
Way Out of Piumb--Turns the Same
Trick With Washington Monument.
Not many people have any idea as to
the enormous amount OF heat that the
sun sends of into space The earth
gets only a very small portion Of 1t
The head of pin placed twenty feet
away from an electric light gets
in proportion to the light on the sur
rounding walls of a room about what
the earth gets of the suns light and
heat radiated into space. Yet that por
ton the earth does get is great enough
to cause great structures to move.
In fact. all stone or metal buildings
are constantly changing their positions
under the hot rays of the sun. The
great dome of the capitol building at
Washington is the largest surface Of
cast iron In the world, and the effect Of
the continuous heat of hot summer
day can best be appreciated, says Har
per's Weekly. when It is known that
this mammoth mass really sways back
and forth under the scorching rays IN
til the top feather In the cap Of the
statue Of Freedom describes an ellipse
the diameter of which on hot day
varies from four to eight inches.
The giant plinth base of the dome.
resting on the roof OF the old sand
stone building, measures 1873 feet on a
side. The greatest diameter OF the
round dome is 125 feet while the
whole iron structure is 21S feet high
from the old capitoPs roof to the base
Of Freedom on the apex. The cast iron
covering this surface is made in thin
sheets. Offering good conductor for
the heat. which swells even the bolts
and beams OF the inside before the sun
has made its circuit
The southern side of the dome suf-
fers most from the heat, being expos
ed longer to the SUM- which passes
south of the zenith while on its jour
ney from the east to the west If the
metal were exposed to a constant
heating the result of the continuation
of such expansion as that received on
very hot days might prove disastrous
but as 1t is little If any permanent in,
jury is done. since the iron returns
regularly to its normal position as the
cool night comes On.
But what seems more remarkable ia
the fact that marble Is also changed In
volume so perceptibly by the sunlight
that the mammoth shaft of the Wash
ington monument 'sways back and
In h. l. H.
outer surface being of hard marble the
expansion Is much greater than II
would be had granite instead of mar
BILE been used. On a hot summer day
the sharp aluminium apex that crowns
the obelisk points to a position at least
four inches north Of normal. but al
ways returns to its proper position in
the cool Of the night.
From the extreme top of the monu-
ment inside long pipe line runs per
pendicularly to the bottom, leading to
a small closet behind the elevator
This contains long pendulum. whose
bob hangs in vessel of mercury.
which prevents its oscillation. Two
stationary transits with highly mag
nifying lenses are focused directly
upon the suspended wire. and through
these each CULVER Of the monument Is
detected. being magniHed on fine
scale graduated to thousandths of an
inch.
Every morning at 10 O'Clock a state
ment Of this plummet line Is taken
and reported to the war department
and it was by this means that the eff
feet which the suns rays have on the
huge white shaft was discovered. This
plumb bob. of course. was placed In
the monument for the purpose of de
tecting any settling it might undergo
and. although the great weight of Its
mass has pressed the ground for many
decades. it has settled only a slight
fraction Of an Inch In one corner.
This seems extraordinary when it is
realized that Its weight of 81, 720 tons
rests on foundation only 1854 feet
square and 80 feet deep from a height
almost fifteen times that of the depth
The whole rests on the sandy bank OF
the Potomac river, with the enormous
pressure of Eve tons to the square
foot. Not only does the sums heat
sway the big obelisk, but at times
when a stir winter gale was blowing,
1t has been reported as much as two
inches out Of plumb.