The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1897-08-25
(From the Washington Times. J

Expansion and Contraction.
(From the Washington Times.)
1t is not generally known that the
Washington Monument, which, to most
people, Is symbolical of stability and i'm
mutability, shifts out of the perpendicu-
lar nearly every day. In fact, this
gigantic pile of stone, that has for so
many years been the most conspicuous
landmark of the capital on entering the
city, rarely occupies the same position
twice on two consecutive days. For eight
years, in fact, ever since the monument
has been completed, scientific reading
have been taken three times a day to de-
termine hows.much out of the perpendicu-
lar the monument has DETECTED From
these reading it is apparent that now, and
for many years past, the Washington
Monument has had its capstone circling
around in space anywhere from one to
four inches from were it ought to be.
Let No one imagine from this fact of
the monument getting move on itself
that there is any danger of big shaft top
pling over. 1t is on too firm foundation
for that. The early constructors of the
monument, when it was commenced back
in the forties, did not build upon the
shifting sands. Although the site select
ed was at that time marshy and on the
banks of the placid Potomac, and might
have appeared insecure, they profted by
a lesson from the Bible, and first laid q
g Co. L., 4, 81
that it can be stated almost with certain
ty that the variation of the monument is
not due in any manner to an imperfect
foundation. Scientists do not always
agree as to the real reason of the monu-
ment's variation, but it is generally con-
the winds and to the contraction and ex-
pansion of the stone due to the heat of the
sun.
That there are many prevalent theories
as to the cause of the variation, report
er who set out last week to observe the
phenomena soon discovered. In the
course of one afternoon various theories
were advanced that it was due to the
heat expansion caused by the sum- to the
winds, to the movement of the earth, to
imperceptible earthquake shocks, to mag
netism, and to an erroneous indicator
which failed to register correctly. Several
persons even declared that in spite of
science they did not believe the monu-
ment moved at all.
1t Is much easier to prove that the mon
ument does move than to find out why
it moves There is an apparatus in the
monument now, which was placed there
by Gen. Casey, under whose direction the
monument. was completed, while he was
at the head of the engineer corps of the
army. This consists of very delicate
pendulum, the slightest vibration of
which is recorded by two telescopes with
hair-line perpendiculars in them. This
cylinder of sheet iron, which excludes all
external forces which might affect the
stability of the pendulum. The pendu-
lum is a heavy brass weight, weighing
perhaps twenty pounds, and tits suspend
ed by brass wire which is attached to
a level iron girder exactly ia feet above
the level of the floor of the monument.
This point, ia feet up. is at the centre of
gravity Of the marble shaft. That is, if
it were possible to suspend such a gigan-
tic mass of marble from one single point
where the weight would be equally dis
tributed, that point would be found
where the wire of the pendulum COM
menceS.
1t is easier to understand when it is
explained that of the 81, 72O tons which
are Incorporated in the monument exact
ly one-half of t he weight is above this
point and the other half below. If this
centre of gravity should ever get outsi de
of the base of support-that is, the square
foundation of the monument-the shaft
would fall over. For instance, the shaft
might lean over SO that the centre of the
| of this ia foot
three feet out of plumb and yet remain
stable, but in order for the monument to
fall the centre of gravity would have to
move something over fifteen feet. AS a
matter of fact. the centre of gravity rarely
moves over an inch and a fraction, so that
the danger of the monuments ever falling
is comparatively insignificant.
However, Gen. Casey thought that it
would be wise to detect the first indica-
tion of a variation as soon as it happened
and he therefore introduced the pendu-
lum A, IL protected from wind and
other iniluy.Ices by this cylinder the brass
weight issuspended in a small bucket of
water, in order that it might be free
from unnecessary swaying and still free
to indicate movement. On a support
above the level of the water are placed
two telescopes at right angles to each
other. Both have the hair line perpen-
diculars found in all surveyors telescopes
and both are adjusted so that the pendu
lum wire will drop accurately between
these perpendicular. The telescopes can
be moved SO as to get in line with the
pendulum Whenever it moves. Indicators
ON the telescopes show how much out of
plumb the pendulum is. One Of these
indicators detects the north and south
movement and the other the east and
west vibration.
AS the centre of gravity is but ia feet
above the level, or trifie over one-third
Of the entire height, it follows that the
top stone of the monument moves over
three times the distance covered by the
centre of gravity. 70 be exact, whatever
distance the centre of gravity is out of
the perpendicular should be multiplied by
3,1S9, the number of times ia will null
tiply into 500, the entire height, The
reason is apparent to all who care to work
out the problem. Thus, if the pendulum
shows that the centre of gravity is out of
the ordinary Just one inch a the top stone
to be. The monument officials only
trouble themselves to take the readings Of
the centre of gravity because that is the
rao Jfpo to no 70 ,,l