New-York daily tribune. [volume] (New-York [N.Y.]) 1842-1866, 1857-12-05
ale q hundred and six feet By hundred fec<-
Within this space arc included the refunds e'role

WUnln Snm space kr0 lhoiouo~ s~'
Of eighty seven feet ia diameter, and four smau cir
cles, each of ten feet in the corners- cut Oh ~
the rotunda. The remainder Of the rectAnge is
| a mana Of masonry which continues with little
diminuton up to the roof arches Of the attic
story Above the roof, the wall 10 cir
cular and five feet thick, giving q hOri-
zontsl surface on which the new dome is to
re.t Of fifteen hundred feet. The weight Of that
dome il estimated at fifteen million poasds, which,
equally distributed over this hor zontssurfa'o, would
give ten thousand pounds pressure on each squsre
fost. II has been found By experiment upon the
new brick walls of the Capitol that to crush them
q pressure is required Of hundred and nlnety-swo
thousand pounds to the square foot-a very unusual
we may observe and extraordinary strength. Ii is
4. recognized rule that the steady pressure on a
wall may be carried to tenth part Of the strength
of the weakest part Of it. But the pressure OF tue
new dome according 10 the data above given, Will
be only nineteenth part Of the strength Of the
wall on which il rests, whence, IL Is argued the
safety Of the new dome s established beyond doubt.
So far as it goes this calculation is good enough;
but it does not seem to go to the bottom. The
circular wall, FIVE feet thick, is no doubt able to
bear the weight of the dome; but the alLimportant
question sil remains: Il the structure below, and
10 the foundation on which that structure rests,
able 10 bear the immense weight which the new
dome will impose upon it'
10 order to get at this point little supplements.
~ calculation will be necessary. The rotunda
walls, on the upper surface Of which the dome is
to rest, are, say hundred feet high from the
foundation. They are composed, accord ng to tho
report referred TO- of stone and brick. Brick walls
if is well known weigh about hundred ana tTen-
ty-fye pounds TO the cubic foot, while stone walls
renee from hundred and twenty. five to & hundred
ard ninety pounds. LIST us suppose the whole wall
to weigh on en- average hundred and forty pounds
to the square foot The wal being hundred feet
bgb there will be already re,tiug upon each square
foot Of the bottom part Of 1t weight, exclusive OF
TIE dome, Of fourteen thousand pounds. The add
tiCn Of the dome will bring the pressure up 70
twenty -four thousand pounds Now it can hardly
be supposed that the strength Of these old walls
can come up to the minimum said to have bsen as
cersired BY experiment as the strength Of the new
brick walls, especially SIS, according to the report
settlement has rot bsen perfectly regular. It
would hardIy be safe to estimate the strength of
there old walls Of more than half Of that ascnsed
TO the new ones, namely, ninety.si six thousand
pounds TO the square foot. In that case,
the pressure, after toe erection of the new dome,
upon the bottt 10 of The old wall, instead Of being
nire thousand six hundred pOunds, as thought to De,
according 70 the rate above stated would mount up
to twenty four thousand pour ds-a very dangerous
exces. Even if, leaving cut any allowance for
cracks and settings we suppose the old walls to be
a. unusually stroI the new ones are said 70 be,
still the pressure upon esch square foot at the bot
tom Of the wall will exceed tue recognized limi. OF
safety b, four thousand eight hundred pounds to
each square foot.
1t may be thought that the walls in the corners
of the square, and which are carried up seventy
feet will add something TO the strength of the elf
cuar wall on which the dune is to stand. II so,
the addition Of strength thus obtained can only be
measured by the thinnest part OF this surrounding
wall which, at the points where the circle oil tne
rotuuda approaches the middle Of the sides Of the
tec,spele. cannot exceed SIX and half feet But
L bnlulu DC DUIuc AZ iuAAtu tLos tHOSN t"''S -"
weakened by doorways, aid perhaps BY dues,
10 that the additional sttepgth derived from the
rectangular part Of the wall would rot exceed that
of solid wall all round Ave feet thick. But, take
il AZ ak feet and haf at the bottom and tss feet
at the top and suppose it to bear its Propoftonate
share of the entire pressure ard still that pres
sure ct the bottom would be twenty thousand three
al IN zach foot
which is double that which, according to
our calculation of the strength OF tie old
walls, can be ssfely imposed upon them,
while it 10 still too great under the rules
even IL We allow ~ the OLD walls power
Of resistance equal to that sscrbed to the new ones
This calculation makes DO allowance for the effect
of ST. aims likely to come upon the walls from the tc-
ton Of storms upon the sides Of the dome, which,
from ts size, hight and exposed situation must st
times be very considerable. Even suppose, how
ever, that the wallis should prove strong enough to
sustain the new structure are we qllte certain as
to tie stability of the earth foundation upon which
these walls rest ? The unequal settlement OF she
walls resulting in the cracks and fractures already
referred to, would seem to imply foundation not
Of the fi,mest description. On account Of the RAPID
slope to the west, the foundation would be likely to
be least firm on that side in which case lesnng
might be expected in that direction. We trust
that, before the rev dome is finally erected, the
perOns in charge Of it will make sure that it will
stand. Some additional Congressional inquiry and
investigation, before voting away more money for the
purpose, would at least do no harm.
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