The mountain Democrat., 1863-05-30
Pressure OF the Atmosphere.

Among the ancient philosophers by
pothesis prevailed that "nature abhorred
vacuum" They were led to this con-
clusion by observing that no vacuum ex-
listed in the world. They found that
when tube was placed with one end in
the water and the mouth applied to it at
the other end, the water would rise in the
tube by what is called suction"-a term
still in use, but now better UNDERSTOOD
From this it was understood that nature
abhorred vacuum.
This illusion was dispelled by the erec-
tion of pump at Florence, by which it
was found impossible to raise the water
to the top of the pipe. Astonishment
was excited by the fact, and Galileo being
then alive, he was consulted as to the
cause. Upon measuring the hight Of the
tube it was found to be thirty four feet,
but he could not explain the phenomenon
Torricclli, his illustrious pupil, unravelled
the mystery. Up till that period it was
supposed that the air possessed no weight
Torricclli came to the conclusion that it
did possess weight, and he inferred that
as column Of water had been raised by
suction in tube to the hight of thirty
three icet, if this were due to the weight
and pressure of the atmosphere, it could
in like manner support shorter column
of a heavier fluid than water. As mercu-
ry was known to be nearly fourteen times
heavier than water, he said the atmos-
phcre should support a column of mercu-
ry about two and a-half feet in hight. In
order to test this hypothesis, he took a
glass tube about three feet in length, and
closed it at one end and filed it with
mercury. He then closed its open end
with his finger, and set it in basin Of
mercury. On Withdrawing his finger the
mercury fell six inches in the tube, leav-
ing column of thirty inches standing
above the level of the basin. The upper
six inches in the tube formed a perfect
vacuum, which, in honor Of the inventor,
has been called the "Torrcclian vacuum. "
The cause Of the suspension Of the mercu-
ry in the tube was demonstrated still
more clearly by carrying the apparatus to
the top Of a lofty tower, when the mercu-
ry fell two inches. Thus was disproved
the old hypothesis, Mature abhors a
vacuum" and thus the barometer was
discovered. No such principle as "suc-
ton" exists; it is the pressure of the at
mosphere, not suction" that causes the
water to rise in the inlet tube of a pump.
Pascal first proposed and used the barom-
eter to estimate the hight of mountains,
instead of by direct measurement, as had
been the method formerly. This instru-
ment is now exclusively employed for
such purposes.
The velocity of gases and liquids flow
ing into vacuum is in proportion to their
pressure and density, and the pressure oil
water and air is according to the hight OF
the column. Thus a column of water
thirty-three feet in hight exercises a
pressure of fifteen pounds on the square
inch, which is exactly the pressure exer.
cised by column of air extending to the
hight Of the atmosphere. The atmosphere
increases in rarity as we ascend, because
air is compressible; but water is consid
cred incompressible, and on the top o.
the highest mountain it is as dense as al
the level of the sea. Air flows into vac
uum at the velocity of one thousand three
hundred and forty feet per second; water
from height of thirty three feet-thC
same pressure as the atmosphere-f fows
into vacuum at the velocity Of about
forty-six feet per second.