Catoctin clarion. [volume] (Mechanicstown, Md.) 1871-1940, 1913-12-11
HIGH Ones SAFEST
Facts About Tall Buildings That
Shake.
Delicate Instruments Record Lateral
and Vertical observation-disclosures
Of Seismograph and Trepadome-
ter Used In Suits for Damages.


absolutely at rest. An almost contin-
uOus series of vibrations passes over
New Yorks massive skyline, says the
Sun of that city. The rush of street
traffic, the action of engines and ele-
vators the tricks Of wind pressure are
constantly setting up wave motions
throughout the great structure of
steel and masonry. The fact that
these buildings are, within certain
limits, elastic, Is of course an assur-
ance of their safety. Accidents from
too much vibration are practically un-
heard Of.
The problem of the vibrations is per-
haps nowhere so complicated as in
downtown New York, Here are group
ed, of course, the greatest collection
of sykscrapers to be found anywhere
in the world The constant passing Of
subway trains at the very base Of
these buildings tends to set up vibra-
tons in every direction. The ele-
waited railroads and the surface cars
cause still other vibrations. In every
siderable machinery for running the
elevators and performing other work.
This is usually located in the low
er easements at the roots of the foun-
dations and the waves thus set in mo-
ton travel to the extreme height OF
the structure. The wind pressure Is
another important factor
In order to know exactly how a
building is affected by these vibra-
tiors several extremely delicate instru,
ments have been invented. They are
adaptations of the familiar seismo
graph used to record earthquakes, al
though less complicated and sensitive.
The commoner form, the seismograph,
is used to measure lateral vibrations.
Another machine, the trepadometer.
measures the vertica! vibrations.
Ths general principle of the apparat-
us in both cases is very simple. The
seismograph consists of a metal table
supported by screws so contrived
that the surface may be placed in an
absolutely horizontal position. On
glass on four steel balls, which are
perfectly spherical. Above the glass
plate is an adjustable needle which
passes back and forth along sliding
bar.
A piece of smoked paper Is laid on
the glass and the needle adjusted to
touch the surface. And vibration of
the building is taken up by the steel
balls SO that the glass on them re-
mains absolutely stationary. The
needle, however. vibrates exactly like
the floor beneath it and scratches a
fine, ragged line along the surface of
the smoked paper This line records
the vibration of the building with sci
entitic accuracy
In the trepadometer a heavy weight
is suspended by long vertical string
so delicate that it responds to the
slightest vibration. A long arm car
rying a pen is attached to the lower
section of the spring. A very slight
vibration is magnified by the apparat-
us, and the pen at the end of the arm
- moves ever so slightly up or down.
The pen Is set above sheet of pa
per which is moved by clockwork. The
paper is placed about a drum which
revolves once in "a hours. The irreg
ular line traced by the pen thus re-
cords the vibrations of the building
for one day
The records of these instruments
are used at times in court to decide
damage cases In which the vibration
of buildings figures. There may be
great difference of opinion as to the
damage done by the vibration, but the
records Of the seismograph and trep-
adometer are accepted as accurate. In
a recent case suit was brought to re-
cover damages alleged to have been
caused by the vibration set up by ma
chinery in operation. A number OF
printing presses, it was said, had
caused such vibration that the walls
were finally cracked. Several wit
Desses visited the building, but their
testimony was contradictory. The
true story, however, and the damages
were awarded on this evidence.
The most violent vibrations are
not found in the highest buildings, as
might be imagined, but often in struc-
lures three or four stories high of old
construction. Such buildings are of
solid masonry, and therefore have lit
tie elasticity, and cannot take up the
wave motion. When heavy machinery,
such as printing presses, for instance,
is set in such building, the jar will
be very perceptible on every floor
The structure of the modern sky
scraper is entirely different and far
safer In it the brick or stone is mere
ly a shell hung upon great steel
structure. The steel riveted together
is more or less elastic. A building Of
say 40 stories could vibrate like a 81
ant tuning fork, could even crack and
loosen the brisk and masonry, and yet
not be in danger of being injured.
The vibrations in building may be
shown with spoonful of water in
a small dish A glass dish is better
for the purpose, a watch crystal Is
just the thing Let this be set in any
building in the busy, crowded parts of
the city and you will find frequent
vibration. The test may be made more
delicate by placing a few drops of
mercury in the receptacle. You will