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BAROMETER1639: Galileo Galilei challenge
the “emptiness resistance
Water cannot be pumped under vacuum to a height
greater than 10.2 m
Blaise Pascal's Barrel Experiment
Rouen France C. 1640
From El Museo Popular Published Madrid 1889
https://www.bing.com/images/blob?bcid=SHMxbOJphuYAew
Evangelista Torricelli (1643)
He was a student of Galileo. He replace water with
mercury, a fluid about 13 times denser than water.
Barometer: Greek word "baros" = weight
the air in the atmosphere has a weight equal to the
weight of a water column of 34 feet (10 meters).
mercury column = 760 mm of Hg = 760 torr
We live in a "sea of air" that exerts a pressure
analogous to the pressure of water on submerged
objects.
Project Gutenberg of Canada ebook #403
BAROMETERTorricelli's type experiment in Pisa in 1644
the height of the mercury column is always fixed at
760 mm regardless the shape of the container.
“We live submerged at the bottom of an ocean of the
element air, which by unquestioned experiments is
known to have weight.”
https://catalogue.museogalileo.it/gallery/Torricellian
Experiment.html
Blaise Pascal Paris 1647
Tested the hypothesis of Torricelli and confirmed
(with experiments) that the atmosphere is indeed
responsible for the height of the column of mercury
Unit of pressure pascal (Pa): Pa = 1 N/m2
a fluid about 13 times denser than water
https://www.britannica.com/biography/Blaise-Pascal
Barometer principle
At equal surface area, the mass of the column of
water (10.3 m) is the same that of mercury metal
(760 mm Hg).
The same observation was made by using alcohol
instead of water.
The ratio: "weight of the atmosphere / surface" is a
value equivalent to that of the liquid inside the tube.
https://scied.ucar.edu/sites/default/files/images/lon
g-content-page/torricelli.jpg
BAROMETERAir Pressure measurement (1648)
Florin Périer carried out atmospheric pressure
measurements at different heights at Puy de Dôme
(France).
The column of mercury fell and rose progressively of
about three inches as the ascent and descent were
made.
The Torricelli – Pascal hypothesis is verified.
https://scied.ucar.edu/sites/default/files/images/lon
g-content-page/torricelli.jpg
Equivalent weight of the atmosphere
roughly 1 kg/cm2
Force corresponding to the mass of 1 m2 of air
at the earth surface
f = ma f = mg→
f = (10340 kg) x (9.81 m/s2) = 1.013x105 N
since pressure = Pa = N/m2
pressure = 101.3 kPa
https://chem.libretexts.org/Courses/Valley_City_Stat
e_University/Chem_115/Chapter_7%3A_States_of_
Matter/7.2%3A_Pressure
U-tube pressure gauge
The difference in level in the tube corresponds to the
different pressure between the two openings
∆P in in mm of Hg
https://www.hydraulicspneumatics.com/
BAROMETERRobert Boyle setup (1660)
Used to find the relation between the pressure and
the volume of a gas
V P= constant
https://kaiserscience.wordpress.com/tag/gas-laws/
The ideal gas law